Some people call it the capital of the world, and in some ways it's hard to argue with that label. New York City is so full of interesting sights and sounds that visitors can keep themselves entertained endlessly without ever going more than 10 blocks from their hotel.
One of the wonderful things about visiting New York City is that nearly everything you've ever heard of is on the relatively small island of Manhattan. If you bring good shoes and you've got a bit of time, you can literally walk from nearly any attraction to nearly any other attraction, but the public transportation system is excellent so that will never be needed.