Roosevelt Island

I never knew about this growing up, but Teddy Roosevelt has his own little island in the Potomac River. There are a couple of nice trails, a big statue of the former President, and- bonus!- it's right in the flight path for planes departing from National Airport. Some of the intended peace and quiet is missing, but it is a very pretty place to take a family walk. Dogs are allowed but no bicycles. Park in the lot off of the George Washington Memorial Parkway (in Virginia) and walk over the footbridge.