This was no simple shaft dug into the ground. It was a piece of considered masonry, built on the west side of Carrickmines Castle, and it survived long enough underground to be excavated and recorded in detail before the motorway scheme claimed the landscape around it.

The well was uncovered during archaeological excavations at Carrickmines Castle carried out under licences 00E0525 and 02E1532, with findings published by T. Breen in 2012 as part of the M50 South-eastern Motorway Scheme reports prepared for Dún Laoghaire-Rathdown County Council. It was cut into a sub-circular foundation pit 2.50 metres deep. The walls were built of granite stones of varying sizes, with no external face but seven distinct interior faces, one of which incorporated three granite steps descending toward the water. The top step served as a threshold, formed from two flat granite slabs; the lower steps were cut from single squared blocks. None of the steps showed significant wear, which may say something about how the well was used, or how quickly it fell out of use. The upper courses of the wall were built with corbels, projecting stones that would have angled inward to meet under a central capstone, forming a low domed roof rising roughly 0.40 metres above ground level. The fills of the well, recorded layer by layer, told their own story: animal bones, leather, worked wood, razor shells, periwinkle shells, hazelnuts, and twigs accumulated in the lower waterlogged deposits. Higher up, the finds shifted to post-medieval pottery including Westerwald ware and the bowl of a seventeenth-century clay pipe, suggesting gradual silting over a long period. The uppermost fill appears to represent a deliberate backfilling of the well, after which a wall was built directly over the threshold stones. Just before that wall went up, someone lit a small fire on the threshold, leaving a charcoal-rich deposit on the granite slabs.

The well no longer exists as a visible structure; it was excavated as part of a road scheme and the site is now subsumed by the motorway infrastructure at Carrickmines. The detailed record, however, is preserved in Breen's four-volume excavation report, and the site itself is catalogued under the Sites and Monuments Record reference DU026-005001-. For anyone interested in the broader context, the castle at Carrickmines was a significant south Dublin fortification, and the excavations that preceded the motorway construction produced a substantial body of medieval and post-medieval material. The well, with its stairway, corbelled roof, and layered fills, is one of the more quietly remarkable features to emerge from that work.