If you're looking to get away from the city for a bit, head over to Theodore Roosevelt Island for some fresh air. It acts as a big, open-air memorial to America's 26th president, and the park boasts a number of things to do, like hiking trails, wildlife observation and park ranger guided tours. The tours especially are great, because they teach you all about the island and how it came to be what it is today. The cherry on top of the cake is the huge monument to Roosevelt located in the middle of the park.
If you own a canoe or a kayak, you can paddle around the island or rent one from Georgetown. Regulars love the oasis it lends as a getaway from the city to do these active activities in nature, including running or jogging on one of the few trails.
Park hours are 6 a.m. to 10 p.m.