K.Z.
Chinatown.
Top of Empire State Building.
tons of museums--i personally like the cloisters, it's up in the Bronx, I think. Medieval stuff, nice garden, but I have not been there for ages. check it out online or in AAA tour book first before you go.
Subway rides are always fun. Avoid rush hour.
You might find an open air farmers market or flea market.
I don't know which airport you are flying in to, but at LaGuardia many years ago there used to be what we called "the perpetual motion sculpture" where it hauled a golf ball up to the top of this contraption, then let it fall into, onto, around, through, you name it...all kinds of other things--it would roll around in a stainless steel bowl before falling through the hole in the bottom, bounce down xylophone keys, etc etc. It was GREAT! and not the same every time depending on which path the ball took. The was also one in the NY Port Authority Bus Terminal, not sure if either or both are still there, but well worth a look.
Have fun!
K. Z.