It is built deliberately into an earlier enclosure, pressing against the earthen bank, and its proportions are precise enough to suggest serious intent: an opening just over two metres wide and two metres tall leads into a shallow vaulted interior, the arch formed from voussoir stones arranged in a camber, a technique more typical of refined estate architecture than agricultural building. A brick kerb runs across the base of the opening, a moulded cornice finishes the coping stones along the east face and wraps around short returns to the north and south, and traces of external render still cling to the masonry. Whatever this structure was meant to look like when complete, it was built with some care.

The detail that gives the site its particular interest is the strong possibility that the building material was not purpose-made but salvaged. The architectural fragments here, and others found nearby, are thought to have been reused from a fortified house associated with the same complex of remains. Fortified houses of the post-medieval period in Ireland were substantial structures, built by landed families who required both security and a degree of domestic comfort, and their dressed stonework, cornices, and arch components were valuable commodities long after the buildings themselves fell out of use. The folly at Ardmayle appears to have been assembled, at least in part, from the bones of an earlier and grander building on the same ground. Three lintelled recesses in the rear wall may be put-log holes, the sockets left when the timber scaffolding poles used during construction were removed, suggesting the structure was purpose-built rather than a simple ruin dressed up. The curvilinear rear wall, bowing away from the rectangular front, adds an oddity of plan that sits comfortably within the tradition of estate follies, landscape features designed to please the eye or suggest antiquity rather than to serve any practical purpose.