What it actually sits upon is something considerably older: the buried remains of a medieval round tower that once formed half of one of the most heavily defended gateways in the medieval city. The entrance at Castle Street, today a straightforward passage into the castle complex, was once a formidable arrangement of two flanking round towers, a portcullis, a gate, and a drawbridge positioned roughly midway across the moat. Almost nothing of this structure is visible above ground, which makes it easy to walk through without any sense of what was once overhead.

The gateway, known as Castle Gate, formed the principal entrance to Dublin Castle and was rebuilt in 1617, suggesting the original medieval fabric had deteriorated significantly by the early seventeenth century. The towers were eventually demolished in the eighteenth century, leaving only what lay beneath the surface. Excavations carried out between 1985 and 1986, recorded by Lynch and Manning, uncovered the tower foundations to the north of a large rectangular barbican, a fortified outwork designed to defend a gateway, aligned directly on the main entrance. The western tower's base survives as the foundation beneath the turret of what was the Genealogical Office, now part of the Irish Heritage Trust's management of the castle precinct. The drawbridge, documented by Healy and by Clarke among others, sat roughly in the middle of the moat, a detail that hints at how wide that defensive channel actually was.

The site is accessible as part of a visit to Dublin Castle, which is open to the public and located off Dame Street in the south city. The upper and lower yards can be walked freely for much of the day. The turret above the old Genealogical Office is visible from the upper yard; there is no excavation to see, as the archaeological remains are below ground level, but knowing what lies beneath changes how the space reads. The Bedford Tower, which now gives its name to this part of the complex and stands at the centre of the upper yard, is a later construction and should not be confused with the medieval gate structure, despite the shared name sometimes applied to both features in the literature.