Mattogno's Bunker 5 Follies.

"Bunker 5" was a name given in 1944 to the gas chamber complex earlier known as "Bunker 2". One plausible hypothesis states that "5" in the name meant the 5th extermination complex after the 4 Birkenau crematoria (that, according to one of the two numbering systems in use, were numbered from 1 to 4).