The poor eponymous cairns on Carnmenellis have to squash up with abandoned granite quarries, a farm, reservoir, a mast, a triangulation pillar... But this book has the Copesque idea that the naturally sculptured earthfast boulders that were, are? here still, are its natural predecessors, a naturally sacred spot.
archive.org/stream/earlyracesscotl01leslgoog#page/n22/mode/1up
I think the strange illustration must be from Borlase’s book, as the Heritage Gateway mentions it (and mentions not being able to find the real thing). Several barrows / cairns have been noted up here though.
The interesting-sounding ‘Giant’s Cave’ is on the lower slopes of the hill. But the HG dully says this is really the remains of a post-medieval structure – it’s been dug out beneath a granite slab and is quite a big chamber at 6x6x1.4m.