Ogof Ffynnon Ddu | |
---|---|
Location | Upper Swansea Valley |
Coordinates | 51°49′27″N 3°39′40″W / 51.8243°N 3.6611°W |
Depth | 274.5 metres (901 ft)[1] |
Length | 59 kilometres (37 mi)[2] |
Discovery | South Wales Caving Club 1946 |
Geology | Limestone |
Entrances | 3 |
Access | South Wales Caving Club—see website for details |
Translation | cave of the black spring (Welsh) |
Cave survey | Survey |
Ogof Ffynnon Ddu (Welsh for cave of the black spring), also known informally as OFD, is a cave under a hillside in the area surrounding Penwyllt in the Upper Swansea Valley in South Wales. It is the second longest cave in Wales and the deepest in the United Kingdom.