Irradiated metro is a heavily damaged part of the Washington, D.C. Metro. It consists of the ruined entryway to the Minuteman station, the collapsed entrance to L'Enfant Plaza station, and the tunnels in between.
The tunnel system is lightly radioactive in some places. The stations themselves are collapsed, but there is an access tunnel on the right as you enter the station. Use the local map to make quick work of this area, as most paths lead to dead ends.