This substantial structure, measuring approximately 10 by 5 metres internally with walls about a metre thick, was likely constructed by Archbishop Richard O’Hedian between 1406 and 1440. The tower, built from roughly coursed limestone rubble and topped with a stepped parapet, features some intriguing architectural details, including an angle buttress on the south wall that rises to second-floor level. At its base, a cusped ogee-headed statue niche cleverly echoes the 13th-century trefoil-headed niches found on the cathedral’s exterior.

The interior reveals the tower’s defensive and residential functions across its various levels. A barrel-vaulted roof covers the first floor, whilst the second floor served as a particularly comfortable living space, complete with a cut-stone oculus window in the west wall and remnants of a joggle-jointed limestone fireplace in the east wall. This level was well-protected with several murder-holes and connected to the cathedral through a mural passage, with a steep staircase rising through the west wall. Unfortunately, much of the south wall collapsed during a storm in 1848, but an 18th-century sketch shows it once featured two-light traceried windows on each of the two upper levels.

A fascinating pentagonal tower links the tower house with the cathedral’s crossing-tower, housing a well-lit spiral staircase that descends into the cathedral through a doorway in the south transept. At the top of this staircase, a sculpted stone head wearing a mitre, presumably depicting an archbishop, watches over visitors. Between 1504 and 1525, the structure was further modified when a second floor was built over the cathedral’s nave, creating an upper hall that connected with the tower house; a practical addition that enhanced the building’s residential capabilities whilst maintaining its defensive strengths.