Above the district of Layenkaul (= digging for stones) there is a former pit with 2 tunnels on the slope of the Kahlenberg. Above the large heap of rubble there are still a few foundation walls of the mine buildings.
From the paved bike path you can see the entrance to the tunnel, which you can easily reach through a ford a little further down the stream. The tunnel leads about 60 meters into the mountain.