Question: Of what material is an enclosed bridge made from which can be viewed from the Ponte dela Paglia bridge in Venice, Italy?

Context paragraphs:
Stone Arch Bridge (Minneapolis): The Stone Arch Bridge is a former railroad bridge crossing the Mississippi River at Saint Anthony Falls in downtown Minneapolis, Minnesota.  It is the only arched bridge made of stone on the entire length of the Mississippi River.  It is the second oldest next to Eads Bridge.  The bridge was built to connect the railway system to the new Union Depot, which at that time was planned to be built between Hennepin Avenue and Nicollet Avenue.  The bridge was completed in 1883, costing $650,000 at the time ($ today).  117 Portland Avenue is the general address of the historic complex.

Ponte Vecchio: The Ponte Vecchio ("Old Bridge", ] ) is a medieval stone closed-spandrel segmental arch bridge over the Arno River, in Florence, Italy, noted for still having shops built along it, as was once common.  Butchers initially occupied the shops; the present tenants are jewelers, art dealers and souvenir sellers.  The Ponte Vecchio's two neighbouring bridges are the Ponte Santa Trinita and the Ponte alle Grazie.

Ponte Sant'Angelo: Ponte Sant'Angelo, once the Aelian Bridge or Pons Aelius, meaning the "Bridge of Hadrian", is a Roman bridge in Rome, Italy, completed in 134 AD by Roman Emperor Hadrian, to span the Tiber, from the city center to his newly constructed mausoleum, now the towering Castel Sant'Angelo.  The bridge is faced with travertine marble and spans the Tiber with five arches, three of which are Roman; it was approached by means of ramp from the river.  The bridge is now solely pedestrian, and provides a scenic view of Castel Sant'Angelo.  It links the rioni of Ponte (which was named after the bridge itself), and Borgo, to whom the bridge administratively belongs.

Ponte (rione of Rome): Ponte is the fifth rione of Rome, and is located in Municipio I.  Its name (meaning "bridge" in Italian) comes from Ponte Sant'Angelo, which connects Ponte with the rione of Borgo.  This bridge was built by Emperor Hadrian (and originally named after him "Pons Aelius") in 134 AD to connect his mausoleum to the rest of the city.  Though Pope Sixtus V changed the rione limits so that the bridge belongs now to Borgo, not to Ponte any more, the area has kept its name.  Its logo is obviously a bridge.

Bridge of Sighs: The Bridge of Sighs (Italian: "Ponte dei Sospiri" ) is a bridge located in Venice, northern Italy.  The enclosed bridge is made of white limestone, has windows with stone bars, passes over the Rio di Palazzo, and connects the New Prison ("Prigioni Nuove") to the interrogation rooms in the Doge's Palace.  It was designed by Antonio Contino (whose uncle Antonio da Ponte had designed the Rialto Bridge) and was built in 1600.

Merchandise Mart station: Merchandise Mart is a station on the Chicago Transit Authority's 'L' system, located in the Near North Side neighborhood at 350 North Wells Street in Chicago, Illinois (directional coordinates 320 north, 200 west).  The station is elevated above street level, on a steel structure.  The turnstiles and customer assistant booth of the current station are located on the second level of the Merchandise Mart itself.  This is the main entrance to the station, although there are two fare-card only, unattended entrances atop two long stairways accessed directly from Wells Street, just north of Kinzie Avenue.  The station is constructed mostly of steel, with wooden platforms covered by a canopy most of their length.  There are two side platforms both long enough to support eight-car trains, the longest possible on the CTA system.  The southbound platform is just slightly below the level of the station entrance while an enclosed bridge over the tracks connects to the northbound platform on the opposite side.  The station is fully accessible, resulting in a complicated elevator setup.  The elevator on the southbound platform can lower from the entrance to the platform, as well as go up to the top of the bridge.  Another elevator on the opposite side of the bridge lowers to the northbound platform.

Ponte dei Tre Archi: The Ponte dei Tre Archi (Italian for "Three Arches' Bridge") is one of the main bridges of Venice, Italy, along with the "Ponte delle Guglie", the other bridge spanning the Cannaregio Canal, and the four bridges spanning the "Canal Grande": "Rialto", "Scalzi", "Accademia", and the "Costituzione".  It is located in "Cannaregio" district ("sestiere"), just South of "Rio San Giobbe", linking the "fondamenta San Giobbe", and the South-West area of "Cannaregio", to the "fondamenta di Sacca San Girolamo" and the North-East of "Cannaregio".  As all other Venetian bridges, the "Ponte dei Tre Archi" is a pedestrian walkway.

Ponte della Paglia: Ponte della Paglia is a bridge in Venice, Italy.  The current structure dates from 1847, and the original structure was built in 1360.  The original structure was the oldest stone bridge in Venice.  The name of the bridge is understood to come from boats mooring nearby to offload straw (paglia).  The bridge is a common place from which to view the Bridge of Sighs.

Ponte della Costituzione: The Ponte della Costituzione (English: Constitution Bridge ) is the fourth bridge over the Grand Canal in Venice, Italy.  It was designed by Santiago Calatrava, and was moved into place in 2007 (connecting Stazione di Santa Lucia to Piazzale Roma), amid protest by politicians and the general public.  The bridge was installed in 2008 and opened to the public on the night of September 11, 2008.  The bridge was known as "Quarto Ponte sul Canal Grande" before the official name was adopted to celebrate the 60th anniversary of the Italian constitution in 2008.  Tourists and locals in Venice now refer to it as the Calatrava Bridge (Italian: "Ponte di Calatrava" ).

Ponte Santa Trinita: The Ponte Santa Trìnita (Italian for "Holy Trinity Bridge", named for the ancient church in the nearest stretch of via de' Tornabuoni) is a Renaissance bridge in Florence, Italy, spanning the Arno.  The Ponte Santa Trìnita is the oldest elliptic arch bridge in the world, characterised by three flattened ellipses.  The outside spans each measure 29 m (95 ft) with the centre span being 32 m (105 ft) in length.  The two neighbouring bridges are the Ponte Vecchio, to the east, and the Ponte alla Carraia to the west.

Supporting paragraphs: Ponte della Paglia Bridge of Sighs
Answer: white limestone