This 15th-century McNamara stronghold takes its name from Lis-Aodha-Finn, meaning the Fort of Hugh the Fair, an ancestor of the McNamara Finn clan who first built here. The castle’s tumultuous history saw it repaired by Rory McNamara in the early 1500s before passing to the O’Briens later that century. By 1611 it lay in ruins, only to be rebuilt by William Costello in 1641, likely as a tenant of the Earl of Thomond. Estate records from 1703 describe it in good repair with 19 cabins on its lands, though local tradition holds that lightning struck the tower centuries ago, sending massive blocks of masonry tumbling down; many were subsequently carted away to build nearby field walls and outbuildings.

Today, only the northwest wall survives to its original three storeys, along with small sections of the adjoining walls. The tower house was built from roughly coursed limestone rubble with a distinctive base batter and large quoins at the corners. Visitors can still trace the original layout: a vaulted guardroom protected the entrance through the northeast wall, whilst the ground floor featured splayed windows with segmental heads. The first floor, once supported by wooden beams and topped with a now-collapsed vault, contained a wall cupboard within its window embrasure. Between the first and second floors, a garderobe chamber was lit by a round-headed loop; its chute may have been later converted to a chimney flue during the castle’s final occupation.

The second floor boasted the tower’s finest architectural detail; a two-light ogee-headed window with external hood moulding that would have illuminated the main chamber. Traces of plaster on the first floor walls likely date from the castle’s last period of habitation. The interior now holds substantial deposits of masonry covered in sod, with a mature thorn tree growing in the eastern corner and briars along the southeast side. About 35 metres east-southeast of the ruins, the original castle well still marks the spot where this once-formidable fortress drew its water, a lasting reminder of the McNamaras, O’Briens, and others who called Lissofin home over five turbulent centuries.