The tomb predates the cashel by thousands of years, yet whoever built that circular stone enclosure chose to incorporate the ancient structure into its design, placing it at the north-western edge and highest point of the interior. It is a quietly unsettling arrangement: a monument to the dead, later folded into the domestic and defensive architecture of a society that came long after.

The tomb itself is of a type known as a wedge tomb, a form of megalithic burial monument common in the west of Ireland and dating to the Early Bronze Age. It is oriented east to west, tapering slightly from roughly two metres wide at its western end to about 1.45 metres at the eastern centre, and stands to a minimum height of around 1.5 metres at the west. The southern wall is a single large sidestone over four metres long, with a dressed top edge that slopes gently downward from west to east. The northern wall is formed by two overlapping slabs, and scholars Ruaidhrí de Valera and Seán Ó Nualláin, writing in their 1961 Survey of the Megalithic Tombs of Ireland, suggested the smaller eastern slab may have been a later addition, given its slightly different orientation and the chipping marks visible on its eastern end. The capstone has since split into five pieces, now resting in fragments inside the chamber. The western end of the tomb is partially buried under debris that has spilled from the cashel wall, obscuring what was once its most prominent face. An earlier account from 1901 by antiquarian Thomas Johnson Westropp described a low souterrain, an underground stone-lined passage, running westward from the tomb into the cashel wall, though a visit to the site in 1997 found no trace of it.

The Ballyganner tomb is not an isolated curiosity. Several other sites in the Burren show the same pattern of early medieval cashels built directly adjacent to or over Early Bronze Age ritual structures, among them Creevagh, Caherconnell, and two sites at Lissylisheen. Whether this reflects a deliberate act of appropriation, an expression of ancestral connection, or simple pragmatism in reusing already-cleared ground is not known. The pattern, however, is consistent enough to suggest it was not accidental.