3. Atlantic Avenue Tunnel
The Atlantic Avenue tunnel, which is also known as the Cobble Hill Tunnel, is a former Long Island railroad tunnel under its namesake avenue in Brooklyn. Constructed in 1844, it is the oldest tunnel under a city street in North America. The tunnel closed in 1861, laying dormant until Brooklyn trolley enthusiast Bob Diamond rediscovered it in 1981.
Diamond gave weekly tours of this tunnel for years until the city deemed it too risky — “He’d lug three plastic orange barricades out to the middle of Atlantic Avenue, pry off the manhole cover with a crowbar, and steady a thin ladder into the narrow shaft, the only entrance to the tunnel. Tourists would line up in the middle of the busy road, descending one by one into a tight passageway,” Adrianne Jeffries wrote in The Verge . Diamond believed that there may be an old locomotive behind a wall that blocks off part of the tunnel, though any plans to find out had been shelved, pending a lawsuit that has since been settled. The mystery continues, though Diamond was nearly certain the train is buried there.