This is a fulacht fia, a type of ancient cooking site found in enormous numbers across Ireland, typically dating to the Bronze Age. The mound itself, roughly 22 metres long, 14 metres wide, and rising to about 1.2 metres, is composed of burnt and fire-cracked stone, the accumulated debris of repeated use over what may have been centuries.

The way a fulacht fia worked was straightforward but effective. Stones were heated in a fire, then dropped into a water-filled trough to bring it to boiling point, allowing meat to be cooked without direct exposure to flame. The spent, shattered stones were raked out and discarded beside the trough, building up over time into the characteristic mound that survives today. At Glasshouse, the opening of the horseshoe faces northeast, directly towards a stream fed by the adjacent well, which would have provided the constant water supply the process required. The proximity of a reliable water source is almost universal among these sites, and here the relationship between the well, the stream, and the mound is unusually legible. A circular enclosure recorded to the southeast of the mound suggests the site sat within a broader landscape of activity, though what that enclosure was used for remains unclear from what survives.