Derryowen Castle dates to around 1450-1500 and has witnessed centuries of turbulent Irish history. Originally built by the O’Shaughnessys, it was granted to Murrough O’Brien by Henry VIII in 1543, before passing through various hands during the bloody conflicts of the late 16th and early 17th centuries. The castle saw dramatic episodes including the killing of Sheriff George Cusack by Turlough O’Brien in 1599, multiple sieges during the Nine Years’ War, and various changes of ownership between Irish lords and English loyalists. By 1837, it was described as a square tower standing 116 feet high with spacious rooms, though partially collapsed. When antiquarian John O’Donovan visited in 1839, only the western wall remained intact.

Today, visitors will find just the northwest corner of this once-formidable stronghold, though even these fragments reveal sophisticated medieval architecture. The surviving walls, constructed from regularly coursed limestone rubble with dressed quoinstones, suggest the tower originally measured approximately 12.5 metres east to west and 7.8 metres north to south. The remains show evidence of multiple floors with stone barrel vaults, a spiral staircase (now vanished), and various chambers including a guardroom near the entrance. Architectural details include tall single-light windows with ogee heads, beam holes and corbels that once supported wooden floors, and wall cupboards built into various chambers. The third floor preserves a large fireplace with an unusual mantle design and mysterious corbels above it, possibly used to hold weapons.

The castle’s most dramatic recent chapter occurred in February 1990, when most of the surviving western wall catastrophically collapsed, taking with it a chimney stack that had risen inside the parapet. Before this collapse, photographs from 1980 show the wall still standing tall, complete with intact windows and architectural features that are now lost forever. Despite its ruined state, the remaining masonry tells the story of a sophisticated fortification; features like the drawbar socket beside the robbed-out doorway, murder-hole provisions, and the bartizan at the tower’s angle speak to its defensive capabilities. Traces of an associated bawn wall can still be detected about 15 metres to the west, hinting at the larger defensive complex that once protected this contested borderland between Gaelic and English power.