Personally, I believe the Intrepid Sea, Air and Space Museum is the coolest Museum in New York City. I'm a Military History fanatic and I've always felt like a little kid going to see the Intrepid, which is an Essex Class Air-Craft Carrier. She was commissioned in 1943 and participated in the Pacific Theater of World War II as well as in the Vietnam War. She was decomissioned in 1974 and made into a Museum in 1982.  On the deck is a number of aircraft used between the 40s and the present, as well as the Enterprise Space Shuttle! You can enter the Concorde Supersonic Jet, as well as the USS Growler, the only Ballistic Submarine open to  the public in the world! This Museum is really worth the time to check out if you're interested in the military technology that humans are capable of creating!