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.