Rock Creek Park Trail / Capital Crescent Trail Loop
(2006) This 21-mile loop begins and ends in Georgetown (see map). I got on the Rock Creek Park Trail near the intersection of M Street and Pennsylvania Avenue. Take a left on Rock Creek Trail (heading north toward the bulk of the park). The paved trail follows near the busy Rock Creek and Potomac Parkway. When you come to the tunnel for the Parkway, there is a "by-pass" bike trail that turns to the left toward National Zoo so you don't have to use the very narrow path through the tunnel. The trail is narrow in places and in poor condition in others.
Rock Creek Trail will end in about four miles, so you hop onto Beach Drive and continue to head north for another four miles. Beach Drive is closed on the weekends, so try to ride then. As soon as you enter Maryland (and leave Rock Creek Park), a separate bike trail begins. Cross the East-West Highway and continue on a scenic paved trail about 1/2 mile toward Chevy Chase.
Before you reach town, take a left at the Georgetown Branch Trail sign. You will go down a residential street to a nicely packed dirt/gravel (four miles) Georgetown Branch Trail to the Capital Crescent Trail in Bethesda. There is a Starbucks at one street intersection for refreshment, and Big Wheel Bikes on your left.
The Georgetown Branch Trail ends in central Bethesda near Barnes and Noble. Cross the street to the beginning of the Capital Crescent and ride eight miles to Georgetown through forests, by the C&O Canal, and along the Potomac. In Georgetown, you exit the trail underneath the expressway. Continue underneath the freeway on K Street. Take a left on 26th Street to return to the beginning.
Take supplies to fix a flat, and stop along the way to help folks that are having mechanical problems. Even if you cannot help them, it's a great thing to do.