From the crossroads, it's about 800m to the dolmen. You should be able to see it in an enclosure to the right of the road, not long after a 90 degree bend. Just after you think you've passed the dolmen, there's an information board and a gate to the enclosure.
There's another info board within - shot up! The dolmen itself has 4 supporting stones, though the capstone only appears to rest on 3 of them. The capstone is huge - well over 2ft thick.