You'll not get to see Aber Camddwr Ring Cairn unless you're a scuba diver. It was submerged in 1961 when the Nant y Moch Reservoir was created. Another thing to note is this isn't the original location of the Aber Camddwr Platform Cairn. The two sites share the same name, and their original locations are both flooded, but they are totally different sites. Unlike it's neighbour, this site has not been reconstructed on dry land.
The Aber Camddwr Ring cairn was originally thought to have been a round hut, but excavations prior to flooding revealed that it was a ring cairn consisting of a bank of stones, about 6ft wide with a rough external kerb. Unusually there was a gap in the ring to the south. At the centre of the cairn was a, 'neat rock-cut pit containing a collared urn'. Surrounding the urn were six shallow hollows in a ring, each containing 'the dismembered remains of a child burnt in situ and covered in flat slabs'.