Lonely Planet review
Stretching between Georgetown and Bethesda, MD, the constantly evolving Capital Crescent Trail is a fabulous (and very popular) jogging and biking route. Built on an abandoned railroad bed, the 11-mile trail is paved and is a great leisurely day trip. It has beautiful lookouts over the Potomac River, and winds through woodsy areas and upscale neighborhoods. It also links up with the C&O Canal & Towpath and trails through Rock Creek Park.
In Georgetown, the trail begins under the Key Bridge on Water St (which is what K St becomes as it moves west along the waterfront); the trailhead is clearly marked. In Bethesda, it starts at the Wisconsin Ave Tunnel, on Wisconsin Ave just south of Old Georgetown Rd (it’s clearly marked here, too, and accessible from Bethesda Metro station).