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Ogof Tarddiad Rhymney


New member
Hi All,
Can anyone supply me with G.P.S coordinates for this cave, the CUCC website says there is no access control on this cave, and that its in a quarry, but doesn't say where!  :confused:


SO 0850:1410
The cave is situated in the Cwar yr Ystrad quarry. From the village of Trefil proceed north for about 5 km from the Tafarn Ty Uchaf, along an increasingly poor condition road, which slowly swings west. After passing some quarries, the road - now little more than a dirt track - splits. Take the right fork, towards a larger quarry.


New member
Entrance is low down at base of old working face on south side of quarry and is usually walled-up (replace boulders after visit).

Be careful parking your car up there, many thefts have occurred.


Active member
Lifted from Caves of the Central Northern Outcrop

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  As the quarry is no longer active, the cave has open access at present.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.

BC (120) 20
Descent (126) 9; (135) 12
Log 20 Entry No 301096
SWCC (117) 12-13 illus.

cucc Paul

Sorry the discription on CUCC is brief i will expand on it some time. Nasty boulders near the entrance in that cave perfect for shin bashing, also in some of the crawls watch your head as there are quite a few straws and there may still be batts about


Active member
The quarry was used for a scene in the movie version of The Hitchhikers Guide To The Galaxy. For those who have seen the film, it's where Arthur, Zaphod and Ford get smacked in the face by hidden 'swatters' (for use of a better description) flapping up from the ground. To me it looks like the flat area you cross to get to Tarddiad Rhymney (Source of the Rhymney (river) I think) looking away from the main quarry face towards the outer 'rim wall'.


Are the looters bodies still buried under the tipped material?  There was an awful smell when I was there in 1995.