GeoGraph - photograph every grid square

One of the several entrances to the Ogof Ffynnon Ddu cave complex which is the third longest cave network in the UK. This location appears to be labelled "Ffynnon-ddu (Spr)" on Ordnance Survey maps, however, Ffynnon Ddu is actually a little distance away between Grithig Cottage and the River Tawe. Water can occasionally be seen emerging near the cave entrance but only under extreme flood conditions. Although it's not obvious, the entrance is gated and access is administered by the South Wales Caving Club, based at nearby Penwyllt as there are in excess of 40 miles of passageways which are dangerous to explore for the inexperienced SN8515 : 1-10 Powell Street, Penwyllt.