recommendation by gingerbeer
There is nothing like exploring NYC by bike. The Hudson River Greenway provides nice views of the river and takes you all the way around the tip of the island through Battery Park, Financial District, Chinatown, etc. The view of the Brooklyn Bridge from below is amazing! The greenway is safe for even the most timid cyclist but if you are a little braver, venture inward and explore some of the great lower Manhattan neighourhoods.
This bike shop is convenient and offers reasonable rental prices.