Built by Oliver McDonnell in 1207, this fortification remained in McDonnell hands until 1549, before being granted to Daniel O’Dowd in 1603, the first year of King James I’s reign. Historical records from that period paint a picture of a more extensive complex, describing “2 castles, a kitchen and bakehouse within the bawn of Roslee”, though today only the main tower house survives.

The rectangular keep that remains measures approximately 12 metres east to west and 9 metres north to south, with walls over 2 metres thick; a solid three-storey structure with a slight base batter typical of medieval defensive architecture. The original entrance at the north end of the east wall has been blocked up, and visitors now enter through what was once a window embrasure in the centre of the south wall. Inside, about a third of the barrel vault that covers the ground floor has collapsed over the centuries. A clever system of mural stairways provides access between levels: one begins at the north end of the east wall and curves south to reach the first floor, whilst another in the south wall rises directly to the battlements, suggesting that wooden stairs once connected to the second floor.

Each level tells its own story through architectural details. The first floor features a large blocked window in the east wall, with single-light openings in the other three walls and a garderobe tucked into the northwest corner; a reminder that even medieval castle dwellers required some basic comforts. The second floor, lit only by windows in the south and west walls, would have served as private chambers. Late 18th-century drawings show that an adjoining building once stood to the east of the keep, aligned east to west and connected by a bawn wall extending north from the keep’s northwest corner, but these additional structures have long since vanished, leaving only the sturdy tower to mark this strategic coastal position.