The Secret Cave In Central Park That Has Been Sealed Up Since The 1930s

Central Park is known for many things- muggings, picnics, ice skating, the turning of the leaves and the finest horseback riding in NYC, but it was built to be a place for big city folk to keep in touch with nature.
So when Frederick Law Olmstead and Calvert Vaux designed and oversaw construction of Central Park in the 1860s they included natural elements such as waterfalls, ponds, and lots and lots of trees.
But there was one natural element which was there from the very beginning- a narrow cave, believed to be partly carved out by humans, which they discovered while excavating for The Ramble.

Olmstead and Vaux decided to blend the cave into their carefully constructed "wilderness" park and even added a flat stone staircase leading to one of the cave's entrances.

The cave was a big hit with visitors, especially kids, but by the early 1900s it had become a den of iniquity:

In 1904, a man attempted suicide (not the first to take place in the Ramble) on the stone steps—though some believed it was actually attempted murder.
In 1922, artist Alexander MacArthur was sentenced to three months in a workhouse for “behaving improperly” inside the cave, and in 1929, about 335 men were arrested in Central Park for “annoying women”—and the Ramble Cave was one of the preferred spots to do so.

Park authorities sealed off the cave in the 1930s, blending it nicely into the surrounding ramble on one side and bricking it up on the other, and now park visitors walk by Central Park's secret cave unaware it's even there.

See The Secret Cave in Central Park- And Why It Was Sealed at mental_floss