As you drive up the valley heading north thru Iserlohn look to your right across the valley to a small mountain which has a huge Iron Cross statue on it commemorating World War I, I think. Under that is Eisernkreuz Hohle which is privately owned by a man living on the main strasse opposite the cave. He invited us to dinner after giving us permission to visit the cave. It does require rappelling, but is well worth a visit.
At dinner he told us that many people sought shelter in the cave during the allied bombing of the Ruhr Valley in WWII. At that point Hal Lloyd who was with us on the trip commented that his father had been a bomber pilot here at that time. A period of embarrassed silence followed that comment.
I doubt Hal has changed.