The ringfort at Croghan occupies a low rise on a small tongue of land projecting into the south-western shore of Killala Bay, in County Mayo, and at high water the narrow neck of ground connecting it to the mainland goes under, briefly severing it from the surrounding pasture. It is an oddly dramatic circumstance for what is otherwise a quietly eroded earthwork, but it suggests that whoever chose this spot was thinking carefully about both visibility and defensibility.

A rath, the Irish term for a ringfort, is a roughly circular enclosure defined by an earthen bank and ditch, used as a farmstead and residence during the early medieval period, roughly between the fifth and twelfth centuries. This particular example is poorly preserved, its outline reduced to a slightly raised oval area measuring approximately 21 metres on its north-east to south-west axis and between 25 and 28 metres north-west to south-east. What survives of the defining bank is a degraded scarp, running from the north-west around to the south, standing about 1.3 metres high at its tallest point on the northern side. A later field fence cuts across the south-western edge, obscuring part of the circuit entirely. Within the interior, there are traces of what may be a rectangular house in the southern half, though this feature is tentative. The setting is not isolated: a second rath sits just 60 metres to the east on the same headland, and a cluster of three more lies roughly 300 metres to the north-west and north, suggesting this was once a relatively populated stretch of coastline.

The site is in pasture and the ground underfoot reflects that, uneven and potentially wet depending on the season. The tidal behaviour of the connecting neck of land is worth bearing in mind if you plan to walk out to the headland, since the window can close without much ceremony.