Theodore Roosevelt Island is an 88 acre piece of land in the middle of the Potomac River. Maintained mostly as a natural park, the center of the island also has a Teddy Roosevelt Memorial, including a statue of Teddy Roosevelt as well as huge stones with some of his more famous quotes on them (about nature, which he was dogmatic to preserve).
Whether you're a history buff, an outdoorsy hiker, a stroller, or just trying to see the river, TR Island is a great way to experience the Potomac. DC was once a swamp, and this low-lying island with some seasonal flooding is lush with fauna and flora because of it. This is a great way to spend a half day, accessible from DC, VA, and MD.
For a full day excursion, you can grab a boat at the stunning and notorious Key Bridge. Or rent a bikeshare and ride along the Potomac.
Mon-Su: 08:30-20:00