Stolen from....
OGOF TARDDIAD RHYMNI NGR SO 0850 1410 A c1800 feet L 3300 VR Survey page 49. In Cwar yr Ystrad quarry about two miles north west of Trefil village. As the quarry is no longer active, the cave has open access at present. Follow the track through the quarry complex until a line of boulders is met at the entrance of Cwm yr Ystrad Quarry. Park here and then walk into the quarry and bear right for 150 yards until you almost reach some concrete foundations. Just before this, there is a huge mass of rock to your left, like an island in the middle of the quarry. The cave is directly on the otherside. Walk down to the left of this island to the deepest point, then look for a walled up entrance just a few feet up a slope of boulders.
Once through the entrance hole there is immediately a 6 foot drop into a large fossil passage in solid rock which then just heads off in a south- easterly direction into the hill. Generally the passage is some 12 feet wide, but up to 25 feet wide in places, with one or two low areas of breakdown. The speleothems are poorly developed but there are some fine sediment banks which have been well taped off.. About 200 yards along the fossil passage from the entrance, a side passage leads off to the right up a mud ramp. This passes over a few holes to a short streamway, Nant Llwyd, before entering a small chamber. To the right in the chamber, a narrow passage can be followed to enter a larger passage. At its end, the narrower way on to the left reaches a junction. Continuing ahead reaches a short section of the larger passage, Nant Criban. To the left a narrow passage continues to a small chamber, where the way on degenerates. After 500 yards a choke is reached which is around 30 feet long, after which the large fossil passage is met again. However after 150 feet this becomes a low sediment filled crawl in the stream. A bit festerous, but can be followed for 200 yards or so, but goes for a considerably distance.
The stream has been trace to Rhymney Risings which are about 2 miles away. Hence Tardiadd Rhymney - [or Rhymni] source of the Rhymney.
The area is notorious for car thieves. One party even had their car battery stolen, necessitating a long walk back to Trefil. I usually park in the second entrance to the quarry a little further to the south west. Not only is it nearer the cave, but you cannot be seen from the road. However???????????????? claims to have shot two looters! Perhaps this is the answer?
Finally, please make sure you replace the wall at the entrance, when leaving, as quarry companies just hate caves and cavers.
References:
BC (120) 20
Descent (126) 9; (135) 12 (232) 7 Entrance very loose. Look out for falling rocks.
Log 20 Entry No 301096
SWCC (117) 12-13 illus.
