The River Camac, which flows through the south of the city before joining the Liffey, was intercepted at this spot by a weir, and the water redirected northward along a mill race, a narrow artificial channel designed to carry a controlled flow of water to drive machinery. On the 1837 edition of the Ordnance Survey six-inch map, that race is clearly visible running from south to north along the western side of Dr Steevens' Hospital, and beside it sits a building aligned east to west that may well have been a working watermill.

The detail was noted by John de Courcy in his 1996 study of the Liffey and its tributaries, and it is the kind of observation that rewards close attention to historical mapping. The weir that fed the race was positioned to the east of Swift's Hospital, the institution now better known as St Patrick's University Hospital, named in connection with Jonathan Swift, who left his estate towards its founding in the eighteenth century. Dr Steevens' Hospital, opened in 1733 and one of the earliest purpose-built public hospitals in Ireland, stands immediately to the east of where the mill race ran. The building recorded on the 1837 map sits on the eastern side of that race, tucked between the waterway and the hospital boundary, in a position consistent with a structure built to exploit the flow.

Nothing of the mill race or the associated building survives visibly above ground today; this is a site that exists almost entirely in cartographic and documentary record. The most direct way to engage with it is through the 1837 Ordnance Survey six-inch map, which is freely accessible through the OSi or the Irish Historic Maps viewer online, where the race and the building can be traced in relation to landmarks that still stand. If you visit the area around Steevens' Lane and the western boundary of the hospital, the general topography gives some sense of where the channel would have run, though the ground has long since been altered. The Camac itself, much reduced and often culverted in this stretch, continues to flow nearby, a reminder that this part of the city was once shaped as much by moving water as by the institutions built along its banks.