The central island, oval and overgrown, sits quietly among its natural neighbours, and the distinction between the three would be easy to miss from the shore. What gives it away, if you look closely enough, is the partial kerb of large stones visible along its northern edge, stones up to a metre wide, which form the tell-tale outline of a crannog.

A crannog is an artificial island, typically constructed by piling timber, stone, brush, and peat into shallow water to create a raised, defensible living platform. They were built across Ireland and Scotland from the Bronze Age onwards, with many remaining in use well into the medieval period. The Mullatigorry example sits in the broader eastern section of Mount Louise Lake, a subrectangular body of water roughly 400 metres east to west and between 150 and 250 metres north to south. The island itself measures approximately 20 metres by 16 metres and rises about 1.5 metres above the waterline. It may have a natural core beneath the accumulated construction, which would have made it an attractive foundation site to begin with. Ash deposits in the core, and two stone piles noted in the water off the southern shore, suggest deliberate building rather than chance formation. The site was described by Smyth in 1954, and remains one of the quieter entries in Monaghan's archaeological record.