I had no problem at all finding this site - for a change!
Opposite the entrance to Llethr Farm is a metal field gate. From here the Burial Chamber is easily seen in the boundry wall two fields away. To get a closer look all you need to do is go over the metal gate and then over the other gate on the opposite side of the field. Warning - the field would be very boggy when wet. I counted 7 large stones making up the collapsed chamber.
The last place on our summer solstice sojourn, parking can be had further down the road in the proper carpark then a short walk back down the road to the footpath. Once on the footpath, I'm affraid we walked in a circular motion looking at all the field walls (and there were many) for I knew only of this chamber that it was in a wall, worked a treat too.
The whole burial chamber has collapsed, except perhaps the large capstone which is still propped up at one side by the wall, the wall only cuts the place in two on a visual level. the place felt unaffected by the wall
As with Eithbed, you'd not know there was a public footpath here if OS didn't tell you so. About 100m in from the road and lay-by, the enormous capstone lies over its chamber, built into a field boundary wall. Five fallen uprights, all about 6ft tall, lie around, four on one side of the wall and one on the other.
There are other smaller stones around and under the stone that are very likely to have been part of the construction. The capstone is a monster, about 10ft across and like many in the area there's a notable flat end (tooled?) giving it a sort of filled-in D shape, like a fat spearhead.
Although it's in a sorry state, it doesn't take a great deal of imagination to get a vibe for its basic orientation and structure.
Although the siting in a field wall gives you problems in fully appreciating this massive cromlech, it might actually be doing us a favour – it is unlikely to suffer the usual farmer assaults, either being moved or ploughed, and so the archaeology and any burial contents may well be being preserved.
I've not visited Crug-yr-Hwch (aka Mountain Burial Chamber) yet, but I understand it's incorporated into a field boundary (like Tre Wallter Llwyd) with collapsed uprights. It may have been a Portal Dolmen, similar to Pentre Ifan. I get the impression it's not been excavated.
In his book Prehistoric Preseli Figgis suggests that the tomb's position between two small rivers (Foel Drygarn and Crug yr Hwch) might be significant.