SCP-2830-1-C during routine maintenance, Sep. 2005.

Item #: SCP-2830
Object Class: Safe
Special Containment Procedures: SCP-2830-1-A through -O are to be secured in Foundation Garage 020-2830. The only unredacted copy of SCP-2830-3 and the original copy of SCP-2830-4 are to be secured in standard Safe-class files in Regional Headquarters 020-Bēth.
Twice yearly, fifteen SCP-2830-3-Positive drivers and fifteen agents from Local Task Force 020-Bēth ("Cato Nine Tails") are to perform routine checks and maintenance on SCP-2830-1-A through -O to ensure their continued function, followed by travel outlined in Itinerary 2830. Any disturbances or changes noted in SCP-2830-2Δ1 are to be reported to Regional Command, who will be responsible for revising containment procedures and Object Class, if necessary.
Continuing efforts will be made to identify and locate Person of Interest-020830 ("Penrose") and associates and detain them for questioning.
Description: SCP-2830 is the collective designation for a series of objects related to a formerly-operating anomalous luxury transportation collective, known as "the Knowledge," believed to be operational from the mid-1960s to 2005.
SCP-2830-1-A through -O are a series of fifteen Austin FX4 hackney carriages2 which have been modified via extranormal means. There are three primary features shared by all instances of SCP-2830-1:

SCP-2830-1 instances, when driven by SCP-2830-3-Positive individuals, can access a complex series of alternate streets within Greater London, termed SCP-2830-2Δ.
The interior cabins of SCP-2830-1 instances form a shared space, approximately ██,███ sq m in size, termed SCP-2830-2Ξ. Exterior spatial position and driving of SCP-2830-1 is effectively 'uncoupled' from the interior experience.3
Despite the existence of SCP-2830-2Ξ, outside observers, regardless of position, see SCP-2830-1 instances as spatially normal, and see the driver and passengers sitting calmly within. Research into the nature of this effect is ongoing.

SCP-2830-2Δ, pictured on first exploration. SCP-2830-1-E is visible on center-right.

SCP-2830-2Δ is the area which can be accessed via SCP-2830-3-Positive individuals driving SCP-2830-1, a vast and potentially endless series of asphalt streets lined with buildings. The Foundation has, as of yet, not discovered methods of access to SCP-2830-2Δ other than SCP-2830-1, and no travel in SCP-2830-2Δ thus far has indicated presence of life or access by other groups. SCP-2830-2Δ is perpetually dark save for halogen streetlamps approximately every 10 m4. What appear to be buildings, trees, fire hydrants and other street-side accoutrements lining the streets of SCP-2830-2Δ are, in fact, constructed entirely of black asphalt, and display no signs of prior inhabitance or activity by any form of life.
A different portion of SCP-2830-2Δ has apparently been accessed by every incursion, and no attempt to meet other instances of SCP-2830-1 within SCP-2830-2Δ has been successful.5
Photographs taken within SCP-2830-2Δ uniformly display distortion and light refraction not visible to the naked eye. All efforts to map SCP-2830-2Δ have thus far ended in failure, owing to the complex and potentially ever-changing internal topography of SCP-2830-2Δ. Exploration of SCP-2830-2Δ is only to take place with Foundation-approved SCP-2830-3-Positive drivers and Level 1 or above Foundation personnel, and said personnel are to never leave view of the SCP-2830-1 instance they utilized to enter SCP-2830-2Δ.
SCP-2830-2Ξ is the shared space of the interior cabins of SCP-2830-1-A through -O. Approximately ██,███ sq m in size, it consists of a large ballroom, fifteen entry/exit areas (corresponding to SCP-2830-1-A through -O), restrooms, a large kitchen, storage and ███ rooms believed to have been used for lodging. Though wear patterns in SCP-2830-2Ξ suggest it was in active use for between twenty and sixty years, all furnishings and contents of SCP-2830-2Ξ were apparently removed prior to turnover to the Foundation, save one bronze chandelier, one chair, and █,███ non-functioning light fixtures and water faucets, which show evidence of past regular use. It is not known how SCP-2830-2Ξ received water and power when it was in regular use.
The "windows" of SCP-2830-2Ξ's rooms (excepting the fifteen entry/exit areas) are apparently unbreakable and display only still blurred shapes and shine with natural light levels appropriate to the current time in London. No connection between blurred shapes visible and actual locations have yet been discovered, and further destructive testing on SCP-2830-2Ξ has been suspended.
The fifteen entry/exit rooms of SCP-2830-2Ξ are a uniform size appropriate to their corresponding SCP-2830-1 instance's interior cabin, and their windows a display an accurate view of the area around said SCP-2830-1 instance. Within each entry/exit room, momentum and sensations accurate to the motion of its corresponding SCP-2830-1 instance can be felt. The four doors of each entry/exit room lead to the world outside the SCP-2830-1 instance, and the rear door leads to the main ballroom of SCP-2830-2Ξ.
SCP-2830-3 is a ██-page pamphlet displaying memetic/Class-6 ("Some Concern") infohazardous properties. Reading (and understanding) operative phrases on pages 8 and 13 cause an individual to become SCP-2830-3-Positive. SCP-2830-3-Positive individuals display the following traits:

A comprehensive, exact knowledge of streets, businesses and addresses in Greater London, and the most effective methods to wayfind between two or more locations in Greater London.
The ability to navigate SCP-2830-1 instances into, and out of, SCP-2830-2Δ easily. Entering and exiting SCP-2830-2Δ can be done at arbitrary locations seemingly unrelated to the actual real-world physical distance between entry and exit points. This ability cannot be used to guide SCP-2830-3-Negative drivers into or out of SCP-2830-2Δ, and SCP-2830-3-Positive instances cannot elucidate or instruct SCP-2830-3-Negative individuals as to the nature of SCP-2830-1's effects or how they are activated.6

It should be noted that SCP-2830-3-Positivity does not change an individual's ability to drive an automobile or driving skill. Therefore, it is recommended that SCP-2830-3-Positive drivers used for testing are trained and licensed drivers with clear safety records.
Five excerpts (with redaction of the operative phrases on pages 8 and 13) from SCP-2830-3 are presented below.

+ Show excerpts from SCP-2830-3

- Hide excerpts from SCP-2830-3

SCP-2830-4, front.

SCP-2830-4, back.

SCP-2830-4 is a handwritten note purporting to be from a "Penrose," who multiple sources indicate as the founder/operator of "the Knowledge." It was placed on the windshield of SCP-2830-1-A when, on June 5, 2005, SCP-2830-1-A through -O and SCP-2830-3 (in SCP-2830-A's glove compartment) were left in the parking lot of a Foundation-owned facility in Leeds. Overnight footage from the facility, including all backups, is missing. SCP-2830-4 is reproduced and transcribed below.

Friends,
I am known as Penrose. Many — more, I think, than you assume — know of the bloody world of glamour and strange beauty that lurks beneath the everyday.
The Everything-Under-Everything has had its barons, its importers and patrons, for hundreds of years. Us common folk — cab drivers, for instance? — spoke of this world in humble whispers, if we spoke of it at all.
But this new, hidden elite yearned to be recognized. To be waited on. They wanted a higher class of every available service.
For forty years, the Knowledge provided that higher class. Everyday black cars

on the outside, first-class accommodations within. Our Shadowslip Ways took the men and women who bought, sold and lived lives rich with powerful magic all about this city — the beating heart of their world.
But my associates and I agree — we are done. Not because of conflict, or tragedy, no; we have done more than most men ever aspire to. We have made our money, made our friends, and it is time for us to slip away and enjoy it all. We want what we built to be admired. If we gave our goods to our biggest clients, they would sell them, or find new brothers to start the idea of the Knowledge anew. But you? You keep strange and beautiful things in perpetuity. I hope you enjoy our work.
We certainly did.
— Penrose ❊

Footnotes
1. Commonly known as the "Understreets," "Shadowslip Ways." See: Evans, Nathaniel, "Terminology of Minor Groups of Interest in the Greater London Area" Fieldwork: An SCP Foundation Journal (2005): 412.
2. Also called cabs or London taxis.
3. Innerly, Alastair, et al, "Books & Their Covers: 'Complex Uncoupling' and Subjective Interior-Exterior Physical Experiences in SCP-2830 and SCP-███" Observer: An SCP Foundation Journal (2007): 312B.
4. These streetlamps do not appear to require maintenance, but can be removed and damaged. No effort to relocate damaged streetlamps has thus far succeeded, due to the complex nature of SCP-2830-2Δ's topography.
5. All attempts to observe signal flares, fireworks, rockets and other objects sent by teams from other SCP-2830-1 instances have similarly ended in failure.
6. As noted in the Secondary Containment Proposal, it is possible SCP-2830-3-Positive individuals are intentionally withholding this information, or there are other unknown factors to SCP-2830-3-Positivity. As a compromise, Primary Containment therefore stipulates that only fifteen level 0 Foundation staff or contractors are to be SCP-2830-3-Positive at any given time.

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