Beneath the ground floor of Maynooth Castle's keep, excavators in 1996 found not one well but two, one sealed inside the other's history. The first had been infilled, most likely when the ground floor was comprehensively remodelled in the early 15th century, and a second was then opened nearby in the same western half of the keep to replace it. It is a small detail, easy to overlook against the larger drama of everything else found during that dig, but it captures something about the layered and repeatedly reinvented nature of the site beneath what visitors now see.

The 1996 excavation, carried out for Dúchas, The Heritage Service, ahead of the ground floor being converted into an exhibition space, revealed seven distinct phases of occupation compressed into the keep's interior. The earliest was a rectangular prehistoric building, its function unknown, associated with no finds at all, though a stone axe head, an unfinished macehead, and flint waste flakes recovered from later contexts may have originated there. Over those remains came early medieval round houses, each roughly five metres across and built in the post-and-wattle technique, in which upright wooden posts are woven with flexible rods to form walls. One of these houses had a curving wooden stockade attached, and it appears to have been in use at the same time as the site was being farmed, marked by evenly spaced shallow furrows that eventually spread across and obscured the structure entirely. The Anglo-Normans arrived around 1175, raising a sod mound of about a metre in height and building a fenced timber settlement on top of it; finds from that level included an arrowhead, an iron spur, and a scabbard chape, along with pottery identified as Ham Green ware, a type produced near Bristol and commonly found on Anglo-Norman sites in Ireland. The stone keep itself followed, probably in the late 1180s, and it stood in various forms until the Silken Thomas Rebellion of the 1530s left it badly damaged.

The two wells, sandwiched somewhere in that sequence between the 12th-century construction and the 15th-century alterations, sit quietly at the end of that long inventory. The second one, opened when the first was abandoned, was presumably still in use when the castle met its end. Both are now beneath the exhibition floor, out of sight but formally recorded, which is perhaps the most fitting outcome for features that were themselves once buried beneath a replacement.