Gwaun Cerrig Llwydion [Craig Cwareli] is a deleted 730m Nuttall and now exists only as a hill on the Pen y Fan horseshoe walk. It offers great views of Fan y Big, Cribyn, Pen y Fan and Corn Du and it on the main path followed around the Horseshoe so chances are you will naturally summit it if you’re doing the walk.
I’d highly recommend doing the Beacons horseshoe anti-clockwise to get the best constant views and it means this hill is ticked off on the way to the highest point of the walk.
The summit is probably the higher tuft of grass, but there is also a pile of rocks near the spot as well. It is a good part of a really great Beacons walk and highly recommended.