The New York City Downtown Boathouse offers complimentary kayaking every weekend through October at three Hudson River docks. No need to make a reservation; just walk right up and wait in (a bit of a) line. Never kayaked before? Not to worry: The nautical experts provide the equipment and the know-how—although they do ask that you sign a liability waiver and wear a bathing suit, shorts and T-shirt. Kids under 16 must be accompanied in the boat by an adult. Ages 2 and up.