Beneath what is now a completed housing development near Station Road in Portmarnock, County Dublin, archaeologists once uncovered evidence of iron-working, the kind of small, purposeful industrial activity that rarely survives in any form. A smithing hearth, essentially a pit used to heat metal for hammering and shaping, was identified within a large sub-surface ditched enclosure east of the local railway line. The enclosure is gone now, removed in its entirety during a legally licensed excavation carried out in advance of construction. What it contained, however, has been carefully recorded.

The excavation, conducted under licence 16E0613, took place over fourteen weeks beginning in January 2017, with a team of ten archaeologists and six general operatives working the site. The enclosure itself was slightly elliptical, measuring roughly 77 metres east-west by 70 metres north-south externally, with an entrance facing east and a location adjacent to the upstanding Portmarnock mound nearby. The smithing hearth, designated feature C138, was a small roughly circular pit measuring just over 80 centimetres across and less than 40 centimetres deep, positioned in the southern part of the enclosure. Its two fills told a layered story: the lower deposit contained slag and hammerscale, the tiny iron fragments shed during the hammering of hot metal, which together are a reliable indicator of on-site smithing rather than simply the disposal of smithing waste elsewhere. Charred grains of barley and wheat recovered from the same basal fill are thought to have drifted in from nearby grain-drying or kilning activity. The upper fill contained further slag, burnt bone, burnt stone, seashell, and flint, as well as two sherds of Dublin-type ware, a category of medieval pottery produced in and around the Dublin area, though these are considered likely to have entered the fill through later disturbance. The full findings were reported by Gill McLoughlin of Courtney Deery Heritage Consultancy Ltd. in an unpublished excavation report submitted to the National Monuments Service on behalf of Sherman Oaks Ltd.

Because the site has been fully developed and the monument no longer exists in any physical form, there is nothing to visit or locate on the ground. The enclosure, the hearth, and the surrounding archaeology were documented and removed as part of a lawful process of preservation by record, meaning the evidence survives in the excavation report rather than in the earth. For anyone interested in following up, McLoughlin's 2019 report, reference 16E0613, is the primary source, and the site record is held by the National Monuments Service. The Portmarnock mound, which stood adjacent to the enclosure, is a separate monument and remains upstanding east of the railway line.