The watermill that once operated on the floodplain of the Mahore River, roughly 680 metres northwest of the Co. Limerick town of Hospital, has been so thoroughly levelled that its existence is now most clearly confirmed not by anything on the ground, but by a rectangular cropmark visible only in aerial photography. Cropmarks appear when buried stone or disturbed soil affects the growth of grass or crops above them, creating patterns readable from the air that are invisible at ground level. It is a peculiar way to encounter a building, through satellite imagery rather than stonework.

By the time the Ordnance Survey mapped the area in 1840, the mill was already a ruin. The surveyors recorded it as two rectangular structures sitting either side of an L-shaped field boundary, and their Name Books noted it as the "Hospital Old Mill (in ruins)," a name by which it was known locally. A mill race, the artificial channel used to direct water from a river onto a mill wheel with enough force to turn it, was also marked on the 1840 map, running roughly 45 metres to the southwest of the main structures. Researchers have suggested the site may be considerably older than its ruined state implies, and that it could represent a pre-1700 watermill connected to the medieval manor of Hospital, a settlement whose name itself derives from a house of the Knights Hospitaller established there during the medieval period.

The site sits in low-lying pasture and is not marked or interpreted for visitors. Faint traces of the mill race are still discernible in orthoimages taken between 2005 and 2017, around 30 metres to the southeast of the main structure location, and the rectangular cropmark of the easternmost building measures approximately 20 metres by 12 metres. Anyone with a particular interest in landscape archaeology or in tracing the industrial geography of medieval Munster can cross-reference the 1840 OSi six-inch maps with current satellite imagery to orient themselves on the ground. The Mahore River runs 25 metres to the north of the site. There is little to find in the field itself, but knowing what to look for, and why it is no longer there, gives the place a quiet coherence it would otherwise lack.