The castle, marked as ‘Murneen Castle’ on 19th and early 20th century Ordnance Survey maps, commands impressive views across the landscape from northwest to southeast, though rising ground to the south and southwest limits the panorama. Built by the 16th century, this fortress belonged to Richard MacMorys, chief of Clan Morris and descendant of the Anglo-Norman Prendergasts who had established themselves in the region centuries earlier.

The castle’s history takes an intriguing turn in 1585, when MacMorys transferred ownership of Murneen, along with nearby Brees Castle and extensive lands in Clanmorris barony, to Francis Barkley, the Marshall of Connacht. This transaction formed part of the Composition of Mayo, a broader administrative reorganisation of the county, though MacMorys cleverly retained a life interest in Murneen Castle and its lands, continuing to reside there until his death in 1607. Today, visitors can trace the outline of what was once a substantial rectangular structure measuring approximately 11.8 metres north to south and 18 metres east to west, built from mortared limestone rubble with its main entrance centrally positioned in the southern wall.

Though greatly ruined, the castle still reveals fascinating architectural details to those who explore its remains. The eastern half preserves the most substantial portions, including walls that once supported at least one upper storey complete with a garderobe chute still visible at the southeast corner. The ground floor was originally divided into multiple vaulted chambers, likely connected by a central passage leading from a double-gated entrance; evidence of this sophisticated defensive arrangement can still be seen in the surviving wall reveals. The castle sits at the southeastern end of what appears to be a rectangular bailey that takes advantage of a natural linear rise in the landscape, with faint traces of additional earthworks to the west and south first documented by antiquarian H.T. Knox in the early 20th century.