Small entrance in dry valley near track.
Follow the old tramway up from Carreg Haffes farm towards the stone walling and as the path crosses the top of the Dan-yr-Ogof dry valley, look for the entrance a few yards from the track on the right.
This is a vertical pothole 90 metres deep in 5 pitches down to a sump above which a high aven has been climbed.
Wessex Caving Club & SWCC, 1946
SSSI: 0854 Mynydd Du (Mixed)
Dolphin & Low, 1947 (also BCRA Trans 4(1/2), 1977);CPC, 1962