http://www.cavedatabase.co.uk/showacave.asp?id=49
Located in the same quarry as Daren Cilau; a fairly obvious entrance at the foot of the cliff (like Daren). A notable feature is the tight corkscrew squeeze that is encountered not far into the cave. I've been there a few times when people have failed to get through it.
There is a survey in a CSS journal on the caves of the Llangattock Escarpment, which also contains a survey of Ogof Clogwyn. You might have to work hard to track down a copy, though CSS are sure to have some.
A good cave, well worth visiting.