<Page>

                                                                   Exhibit 10.21

NML LOAN NO. C-332558

                                 PROMISSORY NOTE

$35,000,000.00                                          Dated as of May 18, 2001

         For value received, the undersigned, whether one or more in number and
if more than one, then jointly and severally, herein called "Borrowers", promise
to pay to the order of THE NORTHWESTERN MUTUAL LIFE INSURANCE COMPANY, a
Wisconsin corporation, who, together with any subsequent holder of this
Promissory Note, is hereinafter referred to as "Lender", at 720 E. Wisconsin
Avenue, Milwaukee, WI 53202 or at such other place as Lender shall designate in
writing, in coin or currency which, at the time or times of payment, is legal
tender for public and private debts in the United States, the principal sum of
THIRTY-FIVE MILLION and 00/100 DOLLARS ($35,000,000.00) or so much thereof as
shall have been advanced from time to time plus interest on the outstanding
principal balance at the rate and payable as follows:

                  Interest shall accrue from the date of advance until maturity
         at the rate of seven and forty-two hundredths percent (7.42%) per annum
         (the "Interest Rate"), computed on the basis of a 360-day year composed
         of twelve (12) 30-day months.
                  Accrued interest only on the amount advanced shall be paid on
         the first day of the month following the date of advance and on the
         first day of each and every month thereafter (in the amount of
         $216,416.67) until maturity. All installments shall be applied first in
         payment of interest, calculated monthly on the unpaid principal
         balance, and the remainder of each installment shall be applied in
         payment of principal. The entire unpaid principal balance plus accrued
         interest thereon shall be due and payable on January 1, 2006 (the
         "Maturity Date"). All such installments of principal and interest shall
         be paid by the Borrowers to the Lender in accordance with Lender's
         electronic wire transfer instructions.

         Borrowers shall have the right, upon thirty (30) days advance written
notice, to prepay this Promissory Note in full with a prepayment fee. This fee
represents consideration to Lender for loss of yield and reinvestment costs. The
fee shall be the greater of Yield Maintenance (as hereinafter defined) or one
percent (1.0%) of the outstanding principal balance of this Promissory Note.

As used herein, "Yield Maintenance" means the amount, if any, by which

         (i)      the present value of the Then Remaining Payments (as
                  hereinafter defined) calculated using a periodic discount rate
                  (corresponding to the payment frequency under this Promissory
                  Note) which, when compounded for such


                                       1
<Page>

                  number of payment periods in a year, equals the sum of .25%
                  and the per annum effective yield of the Most Recently
                  Auctioned United States Treasury Obligation having a maturity
                  date equal to the Maturity Date (or, if there is no such equal
                  maturity date, then the linearly interpolated per annum
                  effective yield of the two (2) Most Recently Auctioned United
                  States Treasury Obligations having maturity dates most nearly
                  equivalent to the Maturity Date) as reported by THE WALL
                  STREET JOURNAL five (5) business days preceding the prepayment
                  date; exceeds

         (ii)     the outstanding principal balance of this Promissory Note
                  (exclusive of all accrued interest).

If such United States Treasury Obligation yields shall not be reported as of
such time or the yields reported as of such time shall not be ascertainable,
then the periodic discount rate shall be equal to the sum of .25% and the
Treasury Constant Maturity Series yields reported, for the latest day for which
such yields shall have been so reported, as of five (5) business days preceding
the prepayment date, in Federal Reserve Statistical Release H. 15 (519) (or any
comparable successor publication) for actively traded United States Treasury
obligations having a constant maturity most nearly equivalent to the Maturity
Date.

As used herein, "Then Remaining Payments" means payments in such amounts and at
such times as would have been payable subsequent to the date of such prepayment
in accordance with the terms of this Promissory Note.

As used herein, "Most Recently Auctioned United States Treasury Obligations"
means the U. S. Treasury bonds, notes and bills with maturities of 30 years, 10
years, 5 years, 3 years, 2 years and 1 year which, as of the date the prepayment
fee is calculated, were most recently auctioned by the United States Treasury.

Other capitalized terms used herein and not otherwise defined shall have the
meanings opposite such terms as set forth in the Lien Instrument hereinafter
referred to.

Upon the occurrence of an Event of Default (as such term is defined in the Lien
Instrument hereinafter referred to) followed by the acceleration of the whole
indebtedness evidenced by this Promissory Note, or a condemnation or sale under
threat of condemnation of all or substantially all of the Mortgaged Property (as
such term is defined in the Lien Instrument), the payment of such indebtedness
will be deemed to be a voluntary prepayment hereof and such payment will,
therefore, to the extent not prohibited by law, include the prepayment fee
required under the prepayment in full privilege recited above.

         Borrowers shall not have the right to make partial prepayments of this
Promissory


                                       2
<Page>

Note, except as provided by, and in accordance with, the terms of the Lien
Instrument or the Plaza II/III Notes (as defined in the Lien Instrument).

         Borrowers acknowledge and agree that the Interest Rate hereunder shall
be increased if certain financial statements and other reports are not furnished
to Lender, all as described in more detail in the provision of the Lien
Instrument entitled "FINANCIAL STATEMENTS".

         All agreements between the Borrowers and the Lender, whether now
existing or hereafter arising, and whether written or oral, are hereby limited
so that in no contingency, whether by reason of demand for payment or
acceleration of the maturity hereof or otherwise, shall the interest contracted
for, charged or received by the Lender exceed the maximum amount permissible
under applicable law. If, from any circumstance whatsoever, interest would
otherwise be payable to the Lender in excess of the maximum lawful amount, the
interest payable to the Lender shall be reduced to the maximum amount permitted
under applicable law; and if, from any circumstance, the Lender shall ever
receive anything of value deemed interest by applicable law in excess of the
maximum lawful amount, an amount equal to any excessive interest shall, at the
option of the Lender, be applied to the reduction of the principal hereof and
not to the payment of interest or, if such excessive interest exceeds the unpaid
balance of principal hereof, such excess shall be refunded to the Borrowers.
This paragraph shall control all agreements between the Borrowers and the
Lender.

         This Promissory Note is secured by certain property (the "Mortgaged
Property") in the City of Jersey City, County of Hudson, State of New Jersey
described in an Amended and Restated Mortgage and Security Agreement (the "Lien
Instrument") of even date herewith executed by Cali Harborside (Fee) Associates
L.P., a New Jersey limited partnership, Cal-Harbor II & III Urban Renewal
Associates L.P., a New Jersey limited partnership, Cal-Harbor IV Urban Renewal
Associates L.P., a New Jersey limited partnership and Cal-Harbor VI Urban
Renewal Associates L.P., a New Jersey limited partnership to THE NORTHWESTERN
MUTUAL LIFE INSURANCE COMPANY and PRINCIPAL LIFE INSURANCE COMPANY, formerly
known as Principal Mutual Life Insurance Company (the "Co-Investor").

         Upon the occurrence of an Event of Default (as defined in the Lien
Instrument), the whole unpaid principal hereof and accrued interest shall, at
the option of Lender, to be exercised at any time thereafter, become due and
payable at once without notice, notice of the exercise of, and the intent to
exercise, such option being hereby expressly waived.

         All parties at any time liable, whether primarily or secondarily, for
payment of indebtedness evidenced hereby, for themselves, their heirs, legal
representatives, successors and assigns, respectively, expressly waive
presentment for payment, notice of dishonor, protest, notice of protest, and
diligence in collection; consent to the extension by Lender of the time of said
payments or any part thereof; further consent that the real or


                                       3
<Page>

collateral security or any part thereof may be released by Lender, without in
any way modifying, altering, releasing, affecting or limiting their respective
liability or the lien of the Lien Instrument; and agree to pay reasonable
attorneys' fees and expenses of collection in case this Promissory Note is
placed in the hands of an attorney for collection or suit is brought hereon and
any attorneys' fees and expenses incurred by Lender to enforce or preserve its
rights under any of the Loan Documents (as such term is defined in the Lien
Instrument) in any bankruptcy or insolvency proceeding.

         Any principal, interest or other amounts payable under any of the Loan
Documents, not paid when due (without regard to any notice and/or cure
provisions contained in any of the Loan Documents), including principal becoming
due by reason of acceleration by Lender of the entire unpaid balance of this
Promissory Note, shall bear interest from the due date thereof until paid at the
Default Rate. As used herein, "Default Rate" means the lower of a rate equal to
the interest rate in effect at the time of the default as herein provided plus
five percent (5.0%) per annum or the maximum rate permitted by law.

         Notwithstanding any provision contained herein or in the Lien
Instrument to the contrary, no personal liability shall be asserted or
enforceable against (a) the partners of any of the Borrowers, or (b) any
principal, shareholder, trustee, beneficiary, director, officer or advisor of
any partner of any Borrower (collectively, the "Exculpated Parties") by the
Lender in respect of the indebtedness evidenced hereby or secured by the Lien
Instrument (collectively, the "Indebtedness"), this Promissory Note or the Lien
Instrument or any other Loan Document or the making, issuance or transfer
thereof, all such liability, if any, being expressly waived by the Lender and
any successive holder of this Promissory Note and the Lien Instrument; and the
Lender and any successive holder of this Promissory Note and the Lien Instrument
shall accept this Promissory Note and the Lien Instrument upon the express
condition that in the case of the occurrence of an Event of Default, the
remedies of the Lender in its sole discretion shall, except as provided below,
be limited to the Mortgaged Property or the proceeds from the sale of the
Mortgaged Property and the proceeds realized by Lender in exercising its rights
and remedies (i) under the Absolute Assignment (as defined in the Lien
Instrument), (ii) under any of the other Loan Documents, and (iii) in any other
collateral securing the Indebtedness. If such proceeds are insufficient to pay
the Indebtedness, Lender and any successive holder of this Promissory Note will
never institute any action, suit, claim or demand in law or in equity against
the Exculpated Parties for or on account of such deficiency; PROVIDED, HOWEVER,
that the provisions contained in this paragraph

         (i)      shall not in any way affect or impair the validity or
                  enforceability of the Indebtedness or the Lien Instrument; and

         (ii)     shall not prevent Lender from seeking and obtaining a judgment
                  solely against Borrowers, and Borrowers shall be personally
                  jointly and severally liable, for the Recourse Obligations (as
                  hereinafter defined); and


                                       4
<Page>

         (iii)    with respect solely to the Borrowers, shall not be applicable
                  in the event of a violation of any of the provisions of the
                  Lien Instrument following the caption entitled "DUE ON SALE"
                  (I.E., Borrowers shall be personally liable for all of the
                  Indebtedness in the event of such violation) (it is expressly
                  agreed and understood that the Exculpated Parties shall not
                  have or incur any personal liability with respect to this
                  subsection [iii]); and

         (iv)     with respect solely to the Borrowers, shall not be applicable
                  in the event of any breach or violation of the provisions of
                  the Lien Instrument following the caption entitled "OTHER
                  LIENS" (it is expressly agreed and understood that the
                  Exculpated Parties shall not have or incur any personal
                  liability with respect to this subsection [iv]); and

         (v)      with respect solely to the Borrowers, shall not be applicable
                  in the event of any fraud or willful misrepresentation by any
                  Borrower or any general partner of any Borrower regarding the
                  Mortgaged Property, the making or delivery of any of the Loan
                  Documents or in any materials or information provided by any
                  Borrower or any general partner of any Borrower in connection
                  with the Indebtedness (it is expressly agreed and understood
                  that the Exculpated Parties shall not have or incur any
                  personal liability with respect to this subsection [v]).

As used herein, the term "Recourse Obligations" means

         (a) rents and other income regardless of type or source of payment
         (including, but not limited to, CAM charges, lease termination
         payments, refunds of any type, prepayment of rents, settlements of
         litigation or settlements of past due rents) from each Section of the
         Property from and after the occurrence of any default under the Loan
         Documents remaining uncured prior to the Conveyance Date, which rents
         and other income have not been applied to the payment of principal and
         interest on this Promissory Note or to reasonable Operating Expenses of
         the Property,

         (b) amounts necessary to repair any damage to the Mortgaged Property
         resulting from waste or caused by the intentional acts or omissions of
         any of the Borrowers or those acting on behalf of any of the Borrowers
         (PROVIDED, HOWEVER, if Borrowers' failure to comply with the
         Maintenance of Property obligations is due to lack of funds before any
         partnership distributions, then the same shall not constitute waste due
         to intentional acts or omissions),

         (c) insurance loss proceeds and condemnation award proceeds released to
         any of the Borrowers but not applied in accordance with any agreement
         between any of the Borrowers and Lender as to their application,

         (d) amounts necessary to pay costs of investigation and clean-up of
         Hazardous


                                       5
<Page>

         Substances (as such term is defined in the Environmental Indemnity
         Agreement of even date herewith) on or affecting the Mortgaged
         Property,

         (e) damages suffered by Lender as a result of fraud or willful
         misrepresentation in connection with the Indebtedness by any of the
         Borrowers or any other person or entity acting on behalf of any of the
         Borrowers,

         (f) amounts necessary to pay real estate taxes, special assessments,
         utility bills, Operating Expenses and insurance premiums with respect
         to the Mortgaged Property either paid by Lender and not reimbursed
         prior to, or remaining due or delinquent on, the Conveyance Date of
         each Section of the Property,

         (g) any sums expended by Lender in fulfilling the obligations of any
         Borrower as lessor under any lease of any Section of the Property prior
         to the Conveyance Date of such Section of the Property,

         (h) any security deposits of tenants not turned over to Lender prior to
         the Conveyance Date, and

         (i) damages suffered by Lender as a result of misapplication or
         misappropriation of tax reserve accounts, tenant improvement reserve
         accounts, security deposits, prepaid rents or other similar sums paid
         to or held by any Borrower or any other entity or person in connection
         with the operation of the Mortgaged Property.

As used herein, "Conveyance Date" means (i) the later of (a) the date on which
title vests in the purchaser at the foreclosure sale of a Section of the
Property pursuant to the Lien Instrument or (b) the date on which a Borrower's
statutory right of redemption shall expire or be waived or (ii) the date of the
conveyance of such Sections of the Property to Lender and/or Co-Investor in lieu
of foreclosure.

Notwithstanding the foregoing, the present partners in any of the present
Borrowers and any present principal, shareholder, trustee, beneficiary,
director, officer or advisor of any present partner of any present Borrower
shall not have or incur any personal liability for the Recourse Obligations or
for the repayment of the Indebtedness in the event that the limitations on
liability shall become null and void as provided above. Excluded from the
operation of this paragraph is any liability for fraud or willful
misrepresentation pursuant to provision (e) above, upon the occurrence of which
the Borrowers and the general partners of the Borrowers shall remain liable.

         This Promissory Note, together with (i) a promissory note dated as of
December 5, 1995 payable to Lender in the principal amount of $55,000,000, (ii)
a promissory note dated as of December 5, 1995 in the principal amount of
$55,000,000 payable to Principal Life Insurance Company, formerly known as
Principal Mutual Life Insurance Company, and (iii) a promissory note of even
date herewith in the principal amount of $35,000,000 payable to Principal Life
Insurance Company, formerly known as Principal


                                       6
<Page>

Mutual Life Insurance Company are secured PARI PASSU by instruments and
agreements executed and delivered by the Borrowers to The Northwestern Mutual
Life Insurance Company and Principal Life Insurance Company, formerly known as
Principal Mutual Life Insurance Company creating, among other things, legal and
valid encumbrances on and an assignment of all of the Borrowers' interest in any
leases of the Mortgaged Property. Terms used herein which are defined in such
instruments or agreements and not otherwise defined herein have the same
definition as in such instruments and agreements. In no event shall such
documents be construed inconsistently with the terms of this Promissory Note,
and in the event of any discrepancy between any such documents and this
Promissory Note, the terms hereof shall govern. The proceeds of this Promissory
Note are to be used for business, commercial, investment or other similar
purposes, and no portion thereof will be used for any personal, family or
household use. This Promissory Note shall be governed by and construed in
accordance with the laws of the state where the Mortgaged Property is located.

         This Promissory Note may not be changed or terminated orally, but only
by an agreement in writing and signed by the party against whom enforcement of
any waiver, change, modification or discharge is sought. All of the rights,
privileges and obligations hereunder shall inure to the benefit of the heirs,
successors and assigns of the holder hereof and shall bind the heirs, successors
and assigns of the undersigned.

         If any provision of this Promissory Note shall, for any reason, be held
to be invalid or unenforceable, such invalidity or unenforceability shall not
affect any other provision hereof, but this Promissory Note shall be construed
as if such invalid or unenforceable provision had never been contained herein.


                                    CALI HARBORSIDE (FEE)
                                    ASSOCIATES L.P., a New Jersey
                                    limited partnership

                                    By:      Mack-Cali Sub X, Inc., a Delaware
                                             corporation, General Partner

                                             By:    /s/ Barry Lefkowitz  (SEAL)
                                                -------------------------
                                                     Barry Lefkowitz
                                                Executive Vice President &
                                                 Chief Financial Officer


                      (SIGNATURES CONTINUED ON NEXT PAGE)


                                       7
<Page>

                    (SIGNATURES CONTINUED FROM PREVIOUS PAGE)


                                     CAL-HARBOR II & III URBAN
                                     RENEWAL ASSOCIATES L.P., a New
                                     Jersey limited partnership

                                     By:      Mack-Cali Sub X, Inc., a Delaware
                                              corporation, General Partner

                                              By:    /s/ Barry Lefkowitz  (SEAL)
                                                --------------------------
                                                      Barry Lefkowitz
                                                 Executive Vice President &
                                                  Chief Financial Officer


                                     CAL-HARBOR IV URBAN
                                     RENEWAL ASSOCIATES L.P., a New
                                     Jersey limited partnership

                                     By:      Mack-Cali Sub X, Inc., a Delaware
                                              corporation, General Partner

                                              By:    /s/ Barry Lefkowitz  (SEAL)
                                                --------------------------
                                                      Barry Lefkowitz
                                                 Executive Vice President &
                                                  Chief Financial Officer


                                     CAL-HARBOR VI URBAN
                                     RENEWAL ASSOCIATES L.P., a New
                                     Jersey limited partnership

                                     By:      Mack-Cali Sub XI, Inc., a Delaware
                                              corporation, General Partner

                                              By:    /s/ Barry Lefkowitz  (SEAL)
                                                --------------------------
                                                      Barry Lefkowitz
                                                 Executive Vice President &
                                                  Chief Financial Officer


                                       8