When you want to be surprised and not having to pay for it.
When you are bored and eager to have a walk, I suggest you to go to Washington Square. Maybe right now there is not much to see due to the cold days we are having lately (and it is said it is going to be worse in February or March… :S ), but when the good weather comes back, it is a pleasure to walk around this beautiful square.
You can find people doing the most awsome and different things in an open space. In every corner, you will find people eager to play chess, as well as gymnastics or breakdancers that are making a comedy show at the same time with the people that they had made stop and stare at them.
In the warmest days, I saw people swimming in the fountain, something unthinkable in Madrid, but the most shocking thing to me was to find a piano player that had brought a grand piano and was delighting the listeners he had around, while they were sleeping, reading or just enjoying the wonderful music surrounded by a very nice garden. Actually, the squares in New York are the few spots where you can find benches to sit in the city, now I know the strategy that is hidden behind, to gather public for all the artists that live here!!