At Moydrum in County Westmeath, the mound itself was the technology: a thick layer of compacted earth wrapped around a brick-lined ice chamber, insulating it against the Irish summer and keeping whatever was stored inside cold enough to matter. The summer house above was not incidental to this arrangement but appears to have been built at the same time and as part of the same design, the two structures conceived together rather than one added as an afterthought to the other.

The icehouse dates to the late eighteenth or early nineteenth century and sits within a small walled woodland plantation, itself understood to have been planted partly to provide shade and therefore contribute to the cooling effect. Ice was not manufactured here but harvested from a pond immediately to the north-north-east of Moydrum Castle, a pond clearly visible on the 1837 Ordnance Survey six-inch map and now long dried up. The ice was carried down and packed into the chamber through an entrance tunnel on the north-west side of the mound, a narrow brick-vaulted passage just over seven and a half metres long, a little more than a metre wide, and barely tall enough to walk upright through. At its eastern end, the tunnel opens into a small lobby area, floored in redbrick, which would once have been sealed by two doorways. This double-door arrangement almost certainly functioned as an insulating airlock, preventing warm air from flooding the chamber every time someone needed to retrieve ice. Beyond the lobby, a flat-headed doorway leads into the ice chamber itself, which is roughly four and a third metres in diameter and around five and a half metres high. Its lower half is shaped as an inverted cone in redbrick, narrowing downward to concentrate the stored ice, while rubble stonework continues above, the whole thing capped by a circular domed roof. The lobby sits directly beneath the steps of the summer house above, meaning that the everyday social ritual of taking tea or air in a garden folly was taking place just a few feet above a carefully engineered cold store. A walled garden belonging to Moydrum Castle stands 78 metres to the south, and the range of buildings annotated as Hill House on the 1837 map lies immediately south of the walled woodland, giving some sense of how organised and deliberate the wider demesne landscape once was.