This curious feature consists of upright stone slabs, each about 0.75 metres tall, arranged to form two sides of a roughly 4 metre square. A natural rock outcrop completes the third side, whilst the fourth remains open. The structure’s purpose remains unclear, though its distinctive layout and careful construction suggest it held significance for the island’s past inhabitants.

Inside this stone enclosure, two flat slabs lie horizontally against the western wall. Local tradition identifies these as the Mass Rock, likely used for Catholic worship during times when the practice was restricted or dangerous. Such rocks served as makeshift altars across Ireland, particularly during the Penal Laws era when Catholics faced persecution. Nearby, another flat stone bears a distinctive depression that resembles a bullaun; a type of artificial basin commonly found at Irish archaeological sites, often associated with early Christian or pre-Christian ritual use.

Inishtrahull itself occupies a unique position in Irish geography, sitting about 6 miles northeast of Malin Head as Ireland’s most northerly point. This remote Atlantic outpost has witnessed centuries of human activity, from ancient settlers to lighthouse keepers, each leaving their mark on the landscape. The presence of features like The Grave, the Mass Rock, and the possible bullaun stone speaks to the island’s long history as a place of both habitation and spiritual significance, despite its isolation from the mainland.