Length: 4 miles.
Level of Difficulty: Moderate with some hills and urban crossings.
Parking: Lots along Rock Creek Park or in the city.
Website: nps.gov

Length: 185 miles, with easy routes just a few miles long.
Level of difficulty: Easy to moderate in the first 15 miles.
Parking: Parking the Georgetown waterfront and at Great Falls National Park (in Maryland.)
Website: canaltrust.org

Length: 4.6 miles, with connecting trails for a longer ride.
Level of difficulty: Moderate with some hills and sharp turns.
Parking: Savage Park in Savage. Trail entrance is past the ball fields. Also available at Lake Elkhorn.
Website: howardcountymd.gov

Length: 18 miles, but easy starting and stopping points of any length.
Level of difficulty: Easy to difficult (final mile near Mount Vernon is a steep uphill climb).
Parking: At every lot along the trail except Lady Bird Johnson Park and Navy Memorial. Metro accessible via Rosslyn and National Airport metro stations. Website: nps.gov

Gwynns Falls Trail Trailhead 1. There are 9 trailheads total that provide access to parking.

Length: 15 miles; various routes as short as 1 mile.
Level of difficulty: Easy to moderate; mostly urban landscape.
Parking: Available at eight different routes along the trail, or throughout the city.

Website: gwynnsfallstrail.org