Beneath the south side of Peter Street in Waterford city, the excavated remains of a medieval undercroft survive in a state that is, in its own way, quietly revealing. An undercroft is a vaulted or semi-subterranean ground-floor space, typically used for storage beneath a merchant's or burgess's hall above, and this one measured roughly fifteen and a half metres north to south and just over eight metres east to west. It is not a dramatic ruin in any conventional sense, but the details uncovered during excavation tell a precise, domestic story: a substantial stone plinth positioned two metres from the western and southern walls, most likely a base for a timber post supporting the ceiling or floor above; sanitation arranged first outside the building's south wall, then reorganised in a later phase so that a new, stone-lined cess-pit sat inside the south-west corner of the structure itself.

The building may have been constructed around 1470, on land that Thomas Rice granted to a man named John Collyn. That transaction is recorded in the Registrum cantariae S. Salvatoris Waterfordensis, a register associated with a chantry foundation in the city, which preserves a number of such property dealings from late medieval Waterford. The building's north end did not survive intact; cellars dug during the eighteenth or nineteenth century cut through and destroyed that portion. What remained when archaeologists worked the site in the late 1980s and early 1990s, as part of the broader programme of excavations across Waterford between 1986 and 1992, was enough to identify at least two distinct phases of use, the second of which converted what had originally been an external cess-pit into an enclosed annex roughly two and a half metres by five and a half metres. That kind of incremental adaptation, sewage arrangements being quietly folded into the fabric of the building as needs changed, gives an unusually mundane but honest picture of urban life in a prosperous late medieval port.