Look more closely, though, and something is off. There is no doorway set high above the ground, no window openings of any kind. The structure, nearly twelve metres tall and just under three metres in diameter, is apparently solid all the way through. It was never meant to be entered, never meant to shelter anyone. A small plaque on the south-west face settles the matter plainly: "Built in 1776."

This is a folly, a structure raised purely for visual effect, and it belongs to a tradition of deliberate romantic artifice that swept across the estates of eighteenth-century Britain and Ireland. Landowners of the period commissioned sham ruins, ornamental hermitages, and imitation ancient monuments to animate the views from their houses and gardens, sometimes out of genuine antiquarian enthusiasm, sometimes simply as a form of conspicuous aesthetic display. The Castlegar tower, built from roughly coursed and mortared limestone boulders, carries a string course, a projecting horizontal band of stone, just below its corbelled roof cap, where flat stones are layered outward in steps to form a shallow cone. The whole thing is a convincing enough pastiche of early Christian stonework to give a passing walker pause. The tower is thought to be associated with Castlegar House, which sits roughly a kilometre to the north-west, suggesting it once served as a designed landscape feature visible from the house or its grounds.