Gesundbrunnen U-Bahn (underground) station in Berlin retains an extensive World War II air-raid shelter. The network of rooms and passages includes original signage and other equipment. Some of the rooms have been restored with authentic furniture and others are used as exhibition space.
Tours of the shelter (including some in English) are run by Berliner Unterwelten, who also use part of the complex as their headquarters. A highly recommended tour.