Somewhere beneath the polished floor of Waterford's Cathedral of the Holy Trinity, also known as Christ Church, lies the floor of a completely different building, one that was already centuries old when it was demolished in 1773. The stones from its west window were carted out to the Portlaw area with the intention of reassembling them as a decorative folly, a fashionable conceit of the period, but the project was never finished and the stones eventually scattered and disappeared. The cathedral that replaced it, designed by John Roberts and completed in 1779, looks Georgian and feels Georgian, but excavations have repeatedly punched through that surface to find the medieval city underneath: a substantial north-south wall, buried piers, and elaborate column fragments, one of which was brought up and put on display in 1997.

The site's origins stretch back at least to the late eleventh century. The first bishop of Waterford was consecrated at Canterbury in 1096, suggesting a pre-Anglo-Norman foundation, and a new cathedral was raised in the thirteenth century. By the fourteenth and fifteenth centuries it had accumulated at least eight side chapels, documented in the municipal archives. One of these, St Saviour's chapel, was established in 1468 by John Collyn, dean of the cathedral, and its register survives. The building was extensively renovated in 1522, and a late seventeenth-century map reproduced by the Reverend R. H. Ryland in 1824 shows it as a substantial structure with a tower and spire. Six internal monuments recorded by Charles Smith in 1746 no longer exist, though the building retains other medieval material: two sixteenth-century effigies, a collection of sculptural fragments, and the Rice altar-tomb, which features a cadaver effigy. This type of monument, showing the deceased as a decomposing corpse rather than an idealised figure, was a late medieval meditation on mortality that appeared across Ireland and continental Europe. Outside the present church, several sixteenth- and seventeenth-century grave-covers survive, among them an early eighteenth-century stone carved with passion symbols, the instruments associated with the crucifixion.