Historical records from the 1655-9 Down Survey map of Killua parish note that “In Dervotstowne there is a Castle in repaire and some small cabbins”, with the structure depicted as a tower house complete with a tall chimneystack. The castle belonged to Barnaby Hill, recorded as an Irish papist, and appears on the Down Survey map of Delvin barony as a tower house with a small angle tower.

Today, only the northeast angle tower of this once impressive structure survives intact, standing approximately 10 metres high. The rectangular tower, built from undressed limestone, measures 5.7 metres northwest to southeast and 3.8 metres northeast to southwest, with walls 1.2 metres thick. The tower retains three storeys, though much of the main castle chamber it once adjoined has been lost. The ground floor was originally accessed through a doorway, 1.37 metres wide, positioned off-centre in the south wall, whilst a now broken doorway in the north wall once led to the main chamber of the castle.

The remaining tower reveals fascinating architectural details about its original design. The ground floor features a window opening at the west end of the south wall, along with a small rectangular opening with internal splay in the southeast wall and a niche in the northeast wall. Upper floors contain several rectangular window openings; two positioned above the south doorway and two more in the north wall. Slight external projections at the north and west corners indicate this surviving tower was once part of a much larger structure, specifically attached to the northeast corner of a complete tower house that dominated this strategic position in the Westmeath landscape.