Rent a kayak for free at the all-volunteer Downtown Boathouse. The rental only allows you to paddle in their embayment, but you'll get a nice skyline view. Join a tour and you can kayak near the Statue of Liberty, circumnavigate Manhattan, or enjoy a skyline sunset. The Downtown Boathouse has three locations: Pier 40 at Houston Street, Pier 96 at 56th Street and 72nd Street in Riverside Park. For tours, also check with Manhattan Kayak Company and New York Kayak Company, Inc.
The New York Department of Parks and Recreation has developed some 100 miles of "greenways"---car-free, tree-lined paths open for recreation. Take the Manhattan Waterfront Greenway to circle the island of Manhattan. Or pedal from the Upper West Side to Battery Park on the Hudson River Valley Greenway, a path that stretches all the way to Albany, the state capital. Rent a bike at Central Park's Loeb Boathouse or Pier 84 on the Hudson River Greenway. The Parks Department also maintains a few mountain biking trails, including one in Manhattan's Highbridge Park.
One of the most memorable walks in New York City is the 1.13-mile (one-way) trek from Manhattan to Brooklyn via the Brooklyn Bridge. From Manhattan, enter the elevated pedestrian walkway via the ramp off Park Row. Completed in 1883, the stone and steel-cable suspension bridge took 13 years to build. As you cross the East River, take in views of the skyline and admire the structure and aesthetics of the bridge itself.
Walk & Learn
On Big Onion Walking Tours, you'll take in the sights and pace of New York City. Choose from more than two dozen different tours, either by location or theme. Themed tours include the American Revolution, immigrant neighborhoods and labor history. The one- to two-mile walks, guided by history graduate students (described as both informed and irreverent), last about two hours.