Visiting the Intrepid
Our trip to the West Side during Fleet Week got the kids interested in the Intrepid Museum so we came back to visit it officially with the kids.
Of course we had to go see the spaceship (although I think they were less wow-ed after having visited Kennedy Space Center at Cape Canaveral).
By far the coolest part I think was learning about life aboard a submarine and getting to go inside a real submarine!