Replying to In Manhattan Need Ideas

I'm in NYC for spring break. I've got the day mostly to myself and need some ideas of what to do in Manhattan. I know that sounds lame because, for goodness sake, it's Manhattan, but I'm overwhelmed with the amount of things to do. Worse, I did NO research before coming, so I have no ideas. I would prefer it's cheap(ish) and maybe not your regular touristy bullshit unless it's really cool. Can you guys give some suggestions??