Tin, lead, copper and slate were mined in that area for several centuries, but almost all of these quarries were shut down in the 19th and 20th centuries. So with a little research you can find countless abandoned mining sites there. Most of them are just smaller tunnels, hardly longer than 100 meters. But there are also larger mines with several levels and shafts deep in the mountain, like this one.
The main entrance was filled up with stones and earth years ago, today the mine is only accessible through a side tunnel. At its smaller hole, I had to squeeze myself through a narrow gap next to a bent metal door - and once again, being overweight wasn't really helpful ...
The former slate mine consists of at least three levels (I can't say for sure because some of the tunnels had already collapsed and could no longer be explored). At the end of the second basement was a small shelter. One of the deepest level was only accessible via a high and very shaky ladder (I hated climbing it ...). In the upper area, there were also remains of rails and a rusted mining cart.