Though the lake has been reduced to marshy wetland following 20th-century drainage works, this trapezoidal enclosure still bears witness to its former importance. The site, which doesn’t appear on 19th-century Ordnance Survey maps, was first properly documented by Knox in the early 1900s when it was still largely intact. Originally measuring roughly 75 metres across at its broad northern end and narrowing to about 55 metres at the south, the eastern third has since been levelled, leaving only partial remains visible today.

What survives is impressive in its own right: a substantial bank, between 5.5 and 7 metres wide, defines the southern, western and northern boundaries, with an external fosse (or defensive ditch) running alongside. The southern bank rises to 2.4 metres on its inner face, cleverly compensating for the natural slope of the land, whilst scattered stones protruding from various sections hint at original stone facing. The northern defences once aligned with the old lake shoreline, and it’s quite possible that lake water originally filled the protective ditch, adding an extra layer of defence. A curious square projection extends from the northern bank, sloping down across the fosse like a ramp; this may have served as access to the water’s edge for boats moored alongside the enclosure.

The interior slopes gently northward, following the natural topography, and bears the marks of later agricultural use with cultivation ridges running north to south. A gap in the western bank, complete with causeway, might be an original entrance, though an unfinished road from 1848 complicates the picture. According to Knox’s research, this was once a castle of the Anglo-Norman MacJordan Duff Mac Costello family, before passing to Sir Theobald Dillon in the late sixteenth century; a reminder that these earthworks once formed part of a complex political and social landscape in medieval Mayo.