This remarkable structure combines two distinct periods of Irish architecture: a 15th-century tower house joined to a 17th-century fortified mansion. The later building, constructed in 1648, replaced the original medieval halls whilst incorporating the five-storey tower into its western side. An inscription on the original gateway, now relocated to Dromoland, commemorates its builders: “This was built in the year of our Lord 1648 by Conor O’Brien and by Mary Ni Mahone, wife of the said Conor”. Mary, better known as the formidable ‘Maire Rua’, was on her second of three marriages when she oversaw this ambitious project.

The fortified house itself is an impressive rectangular structure measuring nearly 19 metres east to west and 10 metres north to south, with walls up to 1.5 metres thick. Its architectural details reveal the wealth and status of its occupants; the south wall features three grand four-light mullioned and transomed windows on each floor, whilst a round-headed main entrance provides a suitably dignified approach. A stairs tower attached to the northwest corner contains small single and double lights framed in dressed limestone with square hood mouldings, though the internal stairs have long since vanished. The second floor includes a particularly defensive feature: a rectangular bartizan accessed through a doorway in the southwest corner, supported on five corbels and equipped with pistol loops for defence. The building originally rose to include an attic level with a central gable containing a three-light window, and evidence suggests there was once a wall-walk around the perimeter.

The castle remained in the O’Brien family through several generations; Maire Rua’s son Donough lived here until 1684 before moving to Dromoland, and the property passed through his descendants until the mid-18th century. By 1773, it had come into the possession of Charles MacDonnell through his marriage to Catherine O’Brien, but the MacDonnells preferred their residence at Newhall and allowed Leamaneh to fall into disrepair. The castle was likely abandoned as a residence around 1800. Today, visitors can still explore the substantial ruins and the remains of two walled gardens that once flanked the castle, complete with a series of fish ponds to the east. The road running south towards Corofin bears the name ‘Sir Donat’s Road’, commemorating Donough O’Brien who was created a Baronet in 1686 and became known locally as ‘Donat’.