As a runner, I am constantly exploring new trails close to home. I was pleasantly surprised when I discovered the Anacostia Riverwalk Trail. You can enter the path a series of ways, but I usually head towards RFK stadium and connect to the trail there.
This path is almost always empty (unlike the Georgetown waterfront) and runs next to the river. If you continue long enough, you will reach the Navy Yard waterfront area (where you can also enter the path). If you head in the other direction (back towards RFK) and cross one of the bridges, you will end up at the Kenilworth Aquatic Gardens. The path is over 17 miles long and most of it is paved.
There is a huge initiative to clean up the Anacostia River, so do your part and throw away some trash if you see it!