These were not grand structures. They were modest dwellings of a type known as Sunken-Featured Structures, a form of construction in which the floor is dug down into the earth rather than built up from it, creating a semi-subterranean interior that would have been warm and relatively weatherproof. Their presence under King John's Castle in Limerick reframes the site entirely.

The houses came to light during excavations carried out in 1990 and 1991, and their significance was set out by Wiggins in 2001. Described as Ostman-type dwellings, they were built by the Ostmen, the Hiberno-Norse communities who had settled in Irish coastal towns during the Viking age and continued to inhabit them well into the medieval period. According to the excavation findings, these three structures were constructed after the departure of the Anglo-Normans in 1176, placing them in the late twelfth or early thirteenth century. They were arranged in a line to the south of a ringwork ditch, a ringwork being a type of early fortification consisting of a circular bank and ditch rather than a stone structure. The same excavation recorded that the bank and ditch of this earlier ringwork had themselves been disturbed, not by later medieval building work, but by the digging of countermines during the siege of 1642, when Limerick was drawn into the conflicts of the Confederate Ireland period. Layers of military engineering from different centuries had pressed down on top of one another, and the houses sat at the bottom of all of it.

King John's Castle stands on King's Island in Limerick city, and remains open to visitors as a heritage attraction with an on-site museum. The excavated house sites are not visible above ground in any direct way, but the visitor centre engages seriously with the archaeology uncovered during the 1990s dig, and the physical evidence of those layers of occupation and conflict is interpreted on site. For anyone with an interest in urban archaeology or in the Hiberno-Norse presence in Irish towns, the context provided here is unusually concrete. The discovery was described as marking the earliest known house sites of urban Limerick, which gives the unremarkable shape of a sunken floor a significance that goes well beyond the modest footprint it once occupied.