The following is based on developer test content cut from Fallout 3 and has not been confirmed by canon sources.
DLC04zTestDuchessGambitCabin is a test cell in Point Lookout that can only be accessed by using console commands. The console command to enter the room is COC <cell name>. As it can only be accessed by console commands it must also be exited this way (i.e. COC PointLookoutStart).