Hillside anbove Bontddu maybe? If not, above Cwmheisian?
Graigwen said:Wot? No interest after a couple of weeks? Time for clues.
1 Don't bother about the unguessable mine. It is the upper trial level of Rhiw manganese mine near Aberdaron. (About SH 22167 28360).
2 The cave is in south Wales. It is in the dolomitized limestone of the Lower Clydach Valley Subgroup. Although a fairly recent discovery it is on the Cambrian Cave Registry. Although very short, the thickness of flowstone in it demonstrates that in the past a considerable amount of water has flowed move than 50m above the nearby surface river.