A bendy trail that connects the two parts of Rock Creek Park. It runs along Beach Drive and Rock Creek. This trail is great if you have time and want a leisurely ride or run. It is maintained quite well and there are a few restrooms and water fountains along the trail. Be ready, however, as the trail is slightly hilly.
The northern portion of the trail starts at the Needwood Visitors Center on the southeastern side of Lake Needwood. The trail crosses a road every 2-3 miles. It first hits Avery Road, then crosses Norbeck, Viers Mill, and Randolph Road. After that, it begins to run roughly parallel Beach Drive. The trail crosses over Rock Creek a few times. The trail is close to the road and so isn't too isolated. It has picnic tables scattered along some of the local community parks it crosses.
A detailed map from Montgomery County can be found here