The waterfront
Tribeca's western boundary is a river, and the two piers on it are among the most useful public space in Lower Manhattan.
Hudson River Park runs the length of Manhattan's west side, and the stretch along Tribeca is one of its better sections — less crowded than the Chelsea piers, and with a wider range of things actually to do.
Pier 25
The longest pier in the park, and the most active. It carries a mini-golf course, sand volleyball courts, a playground, a skate park and a beach volleyball area, plus moorings for historic vessels. There is a seasonal food and drink operation at the end.
It is busy on summer weekends and almost empty on a weekday morning, when it is one of the best places in Manhattan to sit and look at New Jersey.
Pier 26
The quieter and more interesting one. Pier 26 was rebuilt as an ecological pier, with a tidal marsh and a research area operated in partnership with a university, plus a raised boardwalk that takes you out over the water through native planting.
It is designed to teach you something about the Hudson estuary while you walk on it, and it does. There is also a lawn, and the sunset view is the best in the neighbourhood.
The greenway
The Hudson River Greenway — the protected bike and pedestrian path running the length of the park — passes both piers. It is the busiest bike path in the United States and it is genuinely fast, so if you are walking, stay out of the bike lane. The pedestrian path is separate and parallel.
From here you can ride or walk south to Battery Park and around the bottom of the island, or north the entire length of Manhattan.
Practical notes
Most of the recreational facilities are seasonal and several require booking or a small fee. There is very little shade on either pier. The wind off the Hudson is significant year-round and makes the waterfront noticeably colder than three streets inland, which catches people out in spring and autumn.