Top on any urban explorer’s (and Untapped reader’s) list is getting to see the inside of the Washington Square Park Arch. Occasionally, press get access but as the story goes, we have Dadaist Marcel Duchamp, painter John Sloan and their buddies to thank for the closure. In 1916, they climbed to the top, cooked food, lit Japanese lanterns, fired cap pistols, launched balloons and declared it the independent republic of New Bohemia. Citizens were outraged and the interior door of the arch was sealed.

Today at 3 pm, NYC Parks Commissioner Mitch Silver will take people live on Periscope inside the arch where you’ll get to see the vaulted attic space, which was once used as a NYC Parks office, and the Guastavino tiling, the famous artisan tiles you’ll recognize from Grand Central Terminal, the original City Hall subway station, Ellis Island and other civic spaces throughout New York City. The spiral staircase leads out to a roof, accessible via skylight doors.

Update: In the Periscope stream today, the staff first spoke about the temporary arch that was just about a block away before the current arch was built and about the history of the sculptures and carvings on the arch which are related to the history of United States, New York State and of course New York City. Moving towards the area under the arch, the team showed the temporary memorial to the attacks in Paris. We also learned that the Washington Square Park fountain, dating from 1871 to 1873, was first located in Grand Army Plaza near Central Park.

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Inside, you can see quite clearly that the interior structure of the arch is not marble, but brick, three feet thick. The spiral staircase, with its triangular treads, features the ribbed signature surface of Guastavino tile. There are 102 steps up to the top, with a stop in a secret room that functions mostly as an engineering trick – removing the interior of the arch reduces the pressure on the structure and this construction technique is used in most other arches, like the Arc de Triomphe.

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The team reported that the interior had a dusty, brick smell, and ended up top with a 360 degree view of Washington Square Park Arch and the view up 5th Avenue up to the Empire State Building.

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The NYC Parks Periscope app promises to “explore New York City’s parks, natural areas and recreational facilities with experts on exclusive behind-the-scenes tours.”

Next, read about the Top 10 Secrets of Washington Square Park