There appears to be the outline of a structure directly above the beehive 'tomb' The original entrance into the 'beehive' was very narrow and possibly hidden, the 'tunnel' fougou coming later.
Sound inside of it reverberates and would boom into a structure above it.
As for the niche - a cult of prophesying heads is attested to in the Welsh Mabinigion with Brans head speaking. A short distance from carn euny is an inscribed stone at Men Scryfa dedicated to 'RIALOBRANI CUNOVALI FILI' Rialo considered to be prince (Ri in Irish Gaelic is King) and the second part is Bran. So the name and presumably the context is known in the area.
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