Inside, a long, narrow passage leads to an octagonal chamber 8ft/2.4m across, where artefacts such as human bones, arrowheads and carved stones have been found.
Y tu mewn, mae tramwyfa hir, gul yn arwain at siambr wythonglog 8 troedfedd/2.4m ar ei thraws, lle canfuwyd arteffactau fel esgyrn dynol, pennau saethau a cherrig cerfiedig.