That practical intrusion cuts across the north-eastern corner of the cairn, a reminder that this hillside has been in continuous use, in one form or another, for a very long time.

The monument is a court tomb, one of the oldest megalithic burial types found in Ireland, typically dating to the Neolithic period, roughly 4000 to 3500 BC. Court tombs take their name from an open ceremonial forecourt, usually at one end of the structure, which is thought to have been used for ritual activity before or alongside burial. At Mweelin, the tomb is set within a cairn, a mound of loose stone, measuring approximately 18 metres by 16 metres and still standing to around 1.5 metres in height. The internal gallery runs roughly northeast to southwest, extends some 6 metres in length, and is divided into two chambers by a single stone jamb set transversely across the passage. A well-preserved entrance jamb survives at the northeast end, and what may be a court stone is just visible to the east, though the southeast side of the outer chamber is either obscured or no longer present. An old field wall meets the east corner of the cairn, its origin unrecorded but its presence suggesting the land around the tomb was worked long after the monument's original purpose was forgotten.

The tomb lies within Connemara National Park, which means the broader landscape is accessible, though the monument itself sits off the main visitor paths. The holy well to the southeast, connected to the cairn by that incongruous water pipe cutting through the prehistoric stonework, is recorded separately as a site in its own right, and together the two features make for an unusually layered corner of the hillside, where Neolithic burial practice and local devotional tradition end up in unexpectedly close proximity.