I think the following strange story probably relates to the chambered cairn here?
The Druid of Ach a' bheannaich (i.e. The Druid of the Mound of Blessing or Salutation).
At a short distance to the east of the "Druidical" stones at Acha'bheannaich, parish of Latheron, Caithness, there is a cairn overgrown with heather. In the middle of this cairn there is a small enclosure that closely resembles one of the "Druidical" altars that one may see in various parts of the Highlands. I visited this "Druidical" fane in the winter of 1874. The following legend associated with this tumulus was related to me by one of the Caithness ministers, an intimate friend, now deceased:
"When the principal Druid of that district had become so old and infirm that he could no longer perform the functions of his office, he was burnt alive on this altar as a sacrifice. While he was being offered, the young Druid who had been appointed his successor in office kept going round in the altar-smoke - ex fumo dare lucem-- that he might catch the spirit of his predecessor as it took its flight."
Folklore from the Hebrides. III
Folklore, Vol. 9, No. 1. (Mar., 1898), pp. 84-93.
It's hard to know how to interpret it really. Humour? Pro-Christian propaganda? Real belief? Who knows.
Here there are "two turf-covered cairns some 13.0m in diameter and 1.0m high, very badly mutilated and robbed." In the centre of one cairn you can see three upright slabs, probably the remains of a chamber - maybe the other cairn had/has one too. (RCAHMS record).