The History of the Gerstfeldhohe Bunker's hard to believe the Westwall was so extensive in the KMC area. Note the primary line of fortifications, then the secondary line behind it.  Most of these were exploded after the war but remains are easy to find in the forests of this area, as evidenced by this website!
The construction of the Gerstfeldhohe bunker was begun in 1938 by the Reichsarbeitsdienst, a paramilitary government program similiar to the US Civilian Conservation Corps.  A photo in the museum shows RAD barracks adjacent to the museum. Original plans called for Gerstfeldhohe to be the largest of eleven "A-Werke" bunkers between Aachen and just west of Karlsruhe, with 14 km of tunnels holding a vehicle storage area, field hospital, small railroad, munitions depot, and quarters for 800 men. Construction of the Atlantic Wall in 1940 slowed the project, which eventually stopped altogether after 5 km of tunnels were completed . By 1944 Russians POWS labored in the tunnels; graves of these men remained until the 1950's near Erlenbrunn. Local residents, sometimes up to 700 at a time, used the bunker as a bomb shelter during the air war between Aug 1944 and 15 Mar 1945. Beginning with Operation Nordwind (Northwind), SS troops occupied the bunker from Dec 1944 until the Allies came through in mid-March 1945. The area then came under French administration until the US took over the bunker in the late 1940's.  The US Army contacted the original builders in a bid to reconstruct the bunker, but cost was prohibitive and renovation stopped after a cement floor, electricity, ventilation, and a secure entrance were completed. The bunker was then used intermittently by the Americans to store tank and airplane parts and even field rations up through the Gulf War.
This schematic shows the original plan for the Gerstfeldhohe bunker. The vertical tunnel in the middle and darkened square to the right comprise the museum today.  Note an uncompleted elevator shaft at the end of the central tunnel (top on the schematic) - a steady flow of water pours down the empty shaft in this portion of the bunker. The area off to the left of the entrance (bottom left)was used as stalls and a slaughterhouse by 6.SS.Div.Nord troops!