US Capitol building ruins at the National Arboretum, Washington DC
In 1958 the US Capitol building was renovated. As part of that renovation, 24 of the building's Corinthian columns were removed. They sat in storage until the mid 1980s, when someone got the bright idea of putting them in a park. Thus, they are now arranged in the US National Arboretum, a large park in Northeast DC that's well removed from the National Mall.
A few other loose shots from the arboretum:
BONUS: If you're in DC and you see 3 large, identical helicopters fly overhead, you are looking at the President's flotilla. Obama is either in this picture, or they're on their way to pick him up.