Just west of the B4268 road junction at Pentre Meyrick there is a very bumpy, muddy, rough track. You can just about drive down it and shortly you will see trees to your left - this is where the enclosure is. Park as best you can and walk over to the trees. There is a fairly obvious small bank which runs around the square enclosure under the trees.
Not much else to recommend a visit i'm afraid.
Mynydd Bychan is a little Iron Age (and Roman) settlement. It's right next to Pwllywrach, which is mentioned in the following story from Marie Trevelyan:
In a story formerly attached to Pwllywrach, Glamorgan, it is asserted that one of the huntsmen was approaching the kennels one evening, when he heard the wild barking of dogs in the air immediately above his head. It was twilight, and no animals were at hand. The hounds in the kennels were silent. Presently the unseen dogs barked again, and somebody called out "Tally-ho-ho!" It was more like a wail than a cry. When the sound was repeated the huntsman responded with a wailing "Tally-ho-ho-ho!" The next moment all the pack of hounds in the kennels broke loose, surrounded the huntsman, and tore him to pieces, so that nothing but bones remained. People said it was the revenge of the Cwn Wybyr, whose cry the unfortunate man had imitated. In after-years the peasantry declared that often in the night-time the cries of the huntsman and the baying of hounds could be heard distinctly. It was stated that the huntsman had forgotten to feed the hounds, and they fell upon him and killed him. The kennels were pulled down because of this calamity. The spot is still called "the old kennels." [J. R.]
From 'Folk-lore and Folk-stories from Wales' (1909).