I have managed to find the Dolmen de Sept Saints. Almost as hard to find as Kerluir, this again involved some bramble trampling, gorse avoiding action.
The book I'm using now says this is in a sad state, and since the photo therein was taken it's got worse. The dolmen is completely overgrown, one can just see the stones of the passage and the capstone peering through the vegetation but the situation will only get worse here.
A fairly long passage, that is now uncovered, leads to a very low chamber covered by a capstone. It could be that the chamber was originally deep but has been filled in through time.
I'm going to go now because something large and alive is in these woods and scaring me!
As I fought my way out of the woods I was walking along what I believed to be an overgrown path, however it seems that it may well have been the capstones of the chambers of a second dolmen, totally overwhelmed by the foliage.