The original entrance is still there, a two-metre gap on the eastern side of the bank, flanked by two parallel rows of boulders that run four metres into the interior. Standing at that threshold, you are essentially standing where people entered this enclosure for the better part of a millennium, following a path that was deliberately marked out with stone.

A rath, as this type of monument is also known, is a roughly circular or oval earthwork enclosure, most commonly associated with early medieval Ireland, roughly the fifth to twelfth centuries, and typically interpreted as a farmstead defended by a raised bank and, often, an external ditch or fosse. This example sits on a gentle east-facing slope in pasture at Castletown, Co. Sligo. The oval platform measures 32 metres east to west and 28 metres north to south, enclosed by a bank nearly five metres wide, built from earth mixed with substantial limestone boulders and quartzy conglomerates, individual stones averaging around a cubic metre each. What is notably absent is any fosse visible at ground level; either it was never dug, or it has been filled and levelled over centuries of agricultural use. A modern break through the bank on the north-north-west side, three metres wide, is clearly a later intrusion, probably made to allow livestock through, and it contrasts usefully with the older entrance, which retains its flanking stonework.