In 1938 the ‘Festungspioniersstabes 19’ planned to build two huge bunkers on both sides of the Nims river near Irrel. These so-called B-Werke would have been self-suffucient and heavily armoured. The bunker on the west side of the river was called ‘38410 (Katzenkopf)’, and the bunker on the east side was called ‘38420 (Nimswerk)’. The bunkers are almost identical.
The Nimswerk was armoured with a ’20P7 Sechsschartenturm’ (steel cupola with six embrasures), a ‘Festungsflammenwerfer/FN-Gerät’ (360° rotatable flamethrower) and an ‘M19′ 5 centimeter automatic mortar. It had a ’90P9 Kleinstglocke’ (steel cupola with 5 observation slits) for observation. Unfortunately, most of the armoured parts have been scrapped after the war.
In 1947 the French army dismantled both bunkers. They used a lot of explosives and managed to severely damage the upper storeys, but the lower storeys survived. Then the bunkers were covered. Katzenkopf became a museum and can nowadays be visited (website). The Nimswerk is currently being restored and is not accessible. I don’t know what the current status is or if it will become open to the public.