Blockhouse No. 1 - Credit: Wikimedia Commons
Blockhouse No. 1, colloquially known as The Blockhouse, is a small fort in the North Woods section of Central Park, Manhattan, New York City. Finished in 1814, the Blockhouse is the second-oldest structure in the park, after Cleopatra's Needle, and the oldest surviving structure originally built within the park site. It is located on an overlook of Manhattan schist, with a clear view of the flat surrounding areas north of Central Park. Read more on Wikipedia
Source: en.wikipedia.org