On the Welsh side of the river, slightly upstream from Biblins suspension bridge, there’s a single entrance leading to two nearly horizontal mine adits. One extends straight in for 100 yards, while the other goes for 75 yards. Both passages are approximately 5 feet high and 5 to 6 feet wide, seeming to track a vein of iron in the ceiling. The shorter adit is damp, with a ‘waterfall’ near the entrance showcasing some impressive flowstone formations.