This is a monster of a boulder, propped up on limestone pedestals and partly embedded in the hillside. Was it a burial chamber? Hard to tell, it certainly does just look like a larger version of the many similar sandstone boulder on pedestals seen around the park.
The cup and rings do look pretty convincing from some angles, this is quite a soft stone so perhaps they are just very badly weathered. There definitely is a pair of cup and rings on a small boulder further up the path from the track, even in the unfavourable sunlight and bleached texture of the stone, some carving work was noticeable.
This is signposted off the trail as a 'Boulder Burial Chamber'. I'm a little dubious about that classification. There are many large sandstone erratics in Burren (some of them signposted as well), some having landed on pavement similar to the stones propping this monster up. A little research is needed to see if a burial was actually found at this site.
The stone itself must be at least 50 tons. It's so heavy that the corner stone holding it in place is not just fracturing so much as shattering slowly. There are more stones at the back of the 'burial' that seem to form a sort of cist. Hmmmmm...