Though local tradition attributes the castle to the FitzHenry family, who held another stronghold at nearby Kilcavan, no documentary evidence directly links them to this particular fortress. The rectangular tower, measuring roughly 10 metres by 8 metres, showcases the defensive architecture typical of medieval Ireland, complete with granite quoins, a distinctive base batter, and walls that survive right up to where the wall-walk once stood.

The castle's ground floor entrance, protected by both external machicolation and an internal murder hole, speaks to the violent uncertainties of medieval life. Inside, a clever architectural design unfolds across five floors connected by a mural staircase winding through the thick stone walls. The lower levels served practical purposes; the ground floor with its five embrasures for defence, whilst upper floors housed more comfortable living quarters. The second floor featured window seats, a fireplace, and even a garderobe (medieval toilet) tucked into the northeast corner, complete with a rather ingenious waste disposal chute accessed through what the archaeological survey delightfully terms a "box-niche". Higher floors contained additional garderobes, spy holes, and chambers built into the walls' thickness, whilst large windows on the fourth floor would have flooded the space with light.

Archaeological evidence suggests the tower wasn't a standalone structure; the ghostly outlines of pitched roofs on both the north and south walls indicate attached buildings that once stood 5 to 6 metres high. The presence of a secondary doorway and built-in cupboards hints these additions were used alongside the main tower, though a remote sensing survey attempting to trace a connecting street to a house 100 metres south proved inconclusive. What remains clear is that Black Castle represents a sophisticated piece of medieval engineering, its granite bones still standing strong after centuries on the Wexford flood plain.