The monastery on this wave-battered Atlantic rock sits not on a natural platform but on a series of artificially levelled terraces, carved into a sloping shelf on the eastern and south-eastern sides of the north-east peak. The main terrace alone measures 35.5 metres in one direction and 16.5 metres in the other, and is retained by revetment walls, freestanding barriers of unmortared stone built to hold back the hillside, that rise in places to well over six metres.

The engineering involved is quietly extraordinary. The eastern revetment wall of the upper terrace, which adjoins the main terrace, climbs to a maximum height of 7.5 metres and was constructed with a batter, meaning it leans inward as it rises, a technique that gives it stability under the pressure of the slope behind it. Unusually, both the north and east walls of the upper terrace were built on a loose rubble layer with no proper foundations, a decision that eventually caught up with the structure. By the late nineteenth century the Office of Public Works found the top of the eastern wall had developed a noticeable sag and levelled it off. A further intervention came in the late 1980s during conservation excavation, when a reinforced concrete arch and a drystone-faced buttress were inserted at the wall's base. That same excavation found up to 30 centimetres of rubble and peat had accumulated on the paved surface of the upper terrace. The 32-metre south-eastern retaining wall has its own layered history: a clearly distinct stretch of masonry below the position of St Michael's Church marks OPW repair work carried out in 1891, observed and recorded at the time by both Romilly Allen and T. J. Westropp.

Where the flagged pathway rising from Christ's Valley meets the eastern flight of steps, a lintelled entrance leads into the main terrace through a short passage. Excavation of this entrance revealed it dates to the nineteenth century, and it may have been constructed or adapted when lighthouse keepers were temporarily housed within the monastery buildings. Running south-westward from this entrance, a 47-metre wall terminates in a rectangular tower with the remains of a gabled roof; this too is nineteenth-century work, and served as a latrine for the lighthouse personnel, a prosaic addition to a site that had otherwise changed little in a thousand years.