Hi tjj

As I recall (albeit back in 2006) I just walked up to the dolmen and had an (extended) look. The Bryn-yr-hen-Bobl, a short distance away, was more problematic due to 'insurance'. I therefore wrote to the Marquess and received permission. I understand that gentleman has now passed on, but presumably his descendant has the same appreciation. Drop a note to:

The Marquess of Anglesey,
Plas Newydd,
Llanfair P.G.
Anglesey,
North Wales LL61 6DZ

First time I saw this Dolmen was on a school trip, perhaps you could hang around and wait for a group of kids and just walk in with them.
Perhaps not,
Last time I came here must've been nearly ten years ago, pre digital camera days, hence no pictures by me. We paid to go in, it was if I remember, a ticket to go round the gardens, rather than the big house as well. You have to go past the Dolmen to get to the gardens, the other side of which is Bryn Yr Hen Bobl, on private land to be sure, but there is but one gate and a hundred yards to the chamber.
Not much help I'm sure as it was decade ago, but that's what we did.
The gardens were nice too.

Meic has been pretty recently (September) and got some lovely shots...

If the formal request to access Bryn-yr-Hen Bobl is denied/ignored then there is another way to get to it via a nearby church yard which I used in 2011. See my notes/directions attached to the Bryn-yr-Hen Bobl record. Good luck.