A small square tower stands alone in County Kildare, the sole upright survivor of what was once a functioning priory and hospital, and nobody is entirely certain what it was for. Measuring just 4.5 metres by 4.5 metres, the structure rises through three floors, with a barrel vault over the first, and is built from a mixture of granite, limestone, and sandstone, the smaller stones used as pinnings between the larger coursed blocks. Entry comes through the north wall via a segmented doorway with a pointed rear arch and dressed voussoirs, the individual wedge-shaped stones that form an arch. Getting to the upper floors requires either a ladder or a detour outside to a narrow rounded arched doorway, an arrangement that does nothing to clarify what the tower was actually used for. Its function, in short, remains unknown.

The tower is all that visibly remains of the Priory and Hospital of St John the Baptist at Skenagun, an institution whose origins are obscure even by medieval standards. The earliest surviving reference to it dates to 1284, but by the time of the Dissolution of the monasteries in the sixteenth century it was already described as roofless and ruined. A 1539 document records what had once been there: a church, a belfrey, a dormitory, a tower, two halls, three chambers, land, and a water mill, a sizeable complex for what is now an almost invisible site. Beneath and around the tower there are further suggestions of what lies unexcavated. In the late nineteenth century, a vaulted underground chamber was discovered a short distance to the north-west, possibly a souterrain, the term for a man-made underground passage associated with early medieval settlements. More recently, bones have been found to the south of the tower, and a small limestone grave slab survives in a nearby garden, quiet reminders that this was once a place where people lived, were cared for, and were buried.