Washington: 9th Street Tunnel

Washington: 9th Street Tunnel
Originally uploaded by DCVoyager

Flickr photo by DCVoyager who writes:

There are six tunnels under the National Mall and Capitol grounds: the Amtrak railway tunnel, the 3rd Street tunnel, the Metro tunnel under 7th Street, the 9th Street tunnel, the 12th Street tunnel and the Metro tunnel under 12th Street. Two of the three highway tunnels keep things interesting by incorporating curves into their design. They're like everything else in Washington: you have to know the lay of the land in order to survive.