Fallout 3 locations project
Mason District South is part of the Metro system under the Capital Wasteland. It gains access to the Flooded Metro.
This seems to be the closest route to the Shocker, a special Power Fist. After entering the station, take the only door and continue down the tunnel to the first door on the East. Expect Mirelurks, including several kings, while heading down the stairs. Take the first opportunity to open doors into a tunnel heading East. Watch out for mines while following it to a partially flooded irradiated room with various loot. On top of a barrel is the Shocker and the Shocker Glove note.