There are some things you just can't do in Manhattan. Bungee jumping and gambling, for example. But there are some things you can do, and believe it or not one of them is kayaking--and it's free. With a kayak, life jacket, and a paddle--and a little advice--from the friendly folks at the New York City Downtown Boathouse, even novices can ply the waves of the Hudson every weekend and holiday all summer long.