eriksweeklyphoto posted a reply:
Take a stroll of Roosevelt Island, which sits in the middle of the Potomac River between DC and Virginia. There's a parking lot on the Virginia side of the river. From there a pedestrian bridge from there provides access to the Island (you can see it on the Google Maps link below). In the center of the island is a cool old monument to Teddy Roosevelt (different from the FDR memorial discussed above) and a walking path provides access to the perimeter of the island. The forested island provides some unique views of the city and the trees should be lovely in October.
maps.google.com/maps?q=Roosevelt+Island,+Washington+D.C.&...
--Erik