Undergound Gotham Tour
I had a friend who posted pictures from what looks like a total unusual New York experience- an underground tunnel trip in Brooklyn.
The tours are hosted by Curious Expeditions or by calling for dates 718-941-3160
It's in Brooklyn, on Atlantic Ave and they run tours about 1 Sunday a month (although its getting more popular, so they might be doing them more often).
The tunnel was also recently featured on the History Channels “Cities of the Underground” and the tunnel can be seen in youtube videos here, here, here and here.

