The castle, likely built by the MacDonnells in the 13th or 14th century, stands as a testament to the turbulent history of Connacht, where Gaelic clans fought to maintain their ancestral lands against both rival families and English expansion. The island itself, accessible by boat or, when water levels permit, by foot across a narrow causeway, creates a naturally defensive position that made it an ideal stronghold for centuries.

The castle's remains reveal a typical Irish tower house design; a rectangular keep with thick stone walls that would have risen several storeys, providing both defence and domestic quarters for the ruling family. Archaeological evidence suggests the site may have been occupied even before the current stone structure was built, possibly serving as a crannog or lake dwelling in earlier centuries. The MacDonnells, and later the Bourkes who took control of the castle, used this island fortress to control trade and movement across Lough Conn, one of Mayo's largest lakes and an important waterway in medieval times.

Today, the ruins stand peacefully amongst the island's greenery, their weathered stones slowly being reclaimed by ivy and moss. Local folklore speaks of a tunnel that once connected the castle to the mainland, though no evidence of such a passage has been found. The island offers visitors not just a glimpse into medieval Irish life, but also stunning views across Lough Conn to the Nephin Mountains beyond, the same vista that would have greeted the castle's inhabitants centuries ago.