What survives today is merely a portion of the north wall, rising from foundations that once supported a substantial tower house measuring approximately 12 by 7 metres. The building originally stood at least four storeys high, aligned roughly north to south, with commanding views across the surrounding countryside; the River Nore flows about 70 metres to the northwest through the pastoral landscape below.

According to local historian Carrigan, writing in 1905, the castle remained almost perfectly intact until 1820, when it was largely demolished for its stone. The Purcell family, who held the castle as one of their branch seats, would have entered through a doorway in the north wall that has since been robbed out, though the gun loops that once defended it on either side remain visible. The surviving masonry reveals the building's defensive character and domestic arrangements: corbels at the first, second, and third floor levels once supported wooden floors, whilst flat-headed single lights provided illumination at the first and second storeys. The remains of a window embrasure can still be traced in the northeast angle at first floor level.

Today, visitors to the site will find these architectural fragments surrounded by earthworks in the adjoining field, subtle reminders of the castle's former extent and its associated structures. Though reduced to a single wall, Lismaine Castle continues to mark its territory on the bluff, a monument to both medieval power and nineteenth-century pragmatism, when even the sturdiest fortress could be reduced to a convenient quarry for local building projects.