Surprised nobody from dc chimed in.
There's lots of good training road here. Daily lunch ride at Haine's point, weekend ride up Beach Drive, McArthur Blvd... you just have to know where to go. You can even use the MUP's for long slow distance in the fall and winter when they're empty.
Bike commuting to work is popular here, too, that's a good way to get the miles in.
You're here for four weeks - did you bring your bike? You could check it out.