The structure is compact, barely four metres tall, with internal dimensions not much larger than a wardrobe. Built in the Gothic Revival style around 1860, it has the pointed doorway, arched window, and circular oculus opening that Victorian architects borrowed freely from medieval churches. What lifts it out of the ordinary is that some of its stonework genuinely is medieval, not simply designed to look that way. The arch over the doorway is formed from three voussoirs, the wedge-shaped stones that hold an arch together, which carry rope moulding along their edges, a decorative carved detail consistent with 16th-century workmanship. The jamb stones framing the window above appear to have come from the same original doorway.

The folly was built by Sir Benjamin Chapman of Killua Castle, who was serving as MP for Westmeath at the time and wanted, according to the account preserved with the building, to enhance the appearance of the village. He named it Isaac's Well after Isaac White, a blacksmith who lived beside the spring when the tower went up. Where Chapman sourced the medieval stonework is a question that has not been fully resolved. The dressed stone does not closely match the stonework at Knock Killua Church, a medieval structure on the Killua Castle demesne about 1.5 kilometres away, where the tool-finishing differs noticeably. Local tradition points instead to the Franciscan Friary at Multyfarnham, roughly fifteen kilometres to the north-west, as the origin of the carved fragments. That friary, founded in the 13th century, had a long and complicated post-Reformation history, and its fabric was vulnerable to exactly this kind of dispersal. The similarity of the rope moulding to carved stonework at 19th-century Meedin Church, which also incorporates medieval material, adds a further thread to the puzzle without quite resolving it.

The tower sits close to Clonmellon Lodge and the west entrance to Killua Castle, making it easy to locate on the approach road into the demesne. The spring it was built to house no longer flows, so what remains is essentially a decorative shell, but the carved medieval voussoirs in the doorway arch are clearly visible and worth examining closely for the rope moulding detail that carries this small structure's largest historical question.