Really? I thought it was dead famous. I first heard of it when Joey McLoughlin won the stage in Cardiff (?) on the way to the overall win in the 1986 Milk Race. You can find it on the OS map by following a minor road leaving the B4248 northwards between Brynmawr and Blaenavon. It's in grid squares 2212 and 2312, if I can be so old school. Confusingly, there's also a village called Llanelly a couple of miles to the north on the other side of the Clydach. If that one's not enough, there's something similar, which again I've never taken a bike to, a couple of miles south of Llangattock. That one doesn't even seem to have a name.