It is close enough to the water that, on a clear day, the connection between the people who built it and the sea they lived beside feels almost literal. This is a wedge tomb, a type of megalithic burial monument common in the west of Ireland, characterised by a tapering stone-lined gallery that is wider and taller at one end than the other. At Altar, the chamber measures 3.4 metres in length, narrowing from 1.9 metres at the western end to roughly one metre at the east, formed by two parallel rows of three upright slabs, or orthostats, with at least one roofstone still in position above the eastern end.

When Dr William F. O'Brien excavated the site in 1989, the results were quietly remarkable. No clear evidence for an original covering cairn survived, most likely because of intensive post-medieval agricultural activity and the construction of a road in the early nineteenth century. What did survive, however, were traces of the tomb's construction and use that are unusually vivid. Three fragments of cetacean bone, from a whale or dolphin, had been deliberately deposited within a low stone kerb at the entrance during the building phase. Beneath this kerb, two pits held shattered slaty stone, probably the debris left over from shaping the upright slabs and capstones; two cobble-hammers used in that work were recovered alongside them. At the eastern end of the chamber, a pit held a votive deposit of limpet shells, periwinkle shells, and fish bones, and a scatter of cremated human bone was found near the entrance. Struck flint tools, including end-scrapers and a hollow scraper, turned up in the disturbed ground outside. The combination of construction debris, marine offerings, and human remains gives this small monument an uncommon biographical texture, a record not just of burial but of the act of building and the beliefs that attended it.

The tomb sits beside the road along Toormore Bay and is accessible without any significant approach. As a National Monument in State care, the structure itself is protected, and both roofstones remain visible. The deliberate whale-bone deposit and the votive shells are worth holding in mind when standing at the entrance, given how directly the sea is visible from that spot.