The site at Portmarnock represents one such mechanism, now reduced to little more than wall footings, a sluice gate, and fragments of the revetting that once held its mill pond in shape, a quiet waterside puzzle for anyone who knows what they are looking at.

The story of milling at this spot reaches back to at least the 12th century, when the corn mill and its surrounding lands came under the ownership of the Abbey of St Mary in Dublin. The arrangement held for centuries, and by 1650 a single tide water mill at a place called Connyborough, situated just east of Portmarnock bridge and connected to the shore by a causeway, was the operation that survived. It appears on John Rocque's detailed survey map of 1760, fixing it firmly in the documentary record. The mill's later history was more turbulent. In 1799 Thomas Dickinson of Drumnigh took a lease on the property, promptly demolished what was there, and rebuilt to three storeys. Despite that investment, the mill had fallen idle by 1867 for lack of water power, a particular irony for a structure designed around the sea. A storm damaged it in 1903, it lost its roof by 1912, and the remains were taken down in the 1940s.

What is left today sits near Portmarnock bridge on the north County Dublin coast. Visitors will find the physical evidence modest but legible: the footing of the outer walls, the 19th-century mill race along which water would have been channelled, the sluice gate that once regulated the tidal flow, and partial remains of the pond and inlet walls. The site rewards a low tide visit, when the relationship between the structure and the water it once harnessed becomes easier to read in the landscape. It is not a managed heritage site with interpretation boards, so a little background knowledge, or a copy of Rocque's map for comparison, helps to make sense of the scattered stonework.