Undercrofts of former St Mary's College, beneath & to the rear of The Cloister Hall

The remains of early 19th-century buildings stand above the vaulted undercrofts of the 14th-century East wing of St Mary’s College. Further undercrofts extend to the rear of the buildings, and to the west of the former West wing, with a smaller range adjacent to the river.

The undercrofts are constructed with roughly finished barrel vaults, likely consisting of three vaults beneath the house and outbuilding. Two parallel vaults run immediately behind the house, with an uncertain configuration beneath a high, raised platform extending towards the river. This platform provides access to a tower (listed separately with the walls of the adjacent walled garden), which may have marked the southern end of the former West wing.

The Cloister Hall is a two-storey, three-window house built of roughcast rubble stone, featuring a slate eaves roof and stone end stacks. It has 12-pane sash windows and a central door with four fielded panels. A double flight of steps leads to the front door, rebuilt since 1981. A low rubble garden wall sweeps up to central ashlar piers flanking the steps. A similar pier exists to the right, with the wall continuing as a retaining wall to the northeast corner of the outbuilding. A basement entrance to the undercrofts is located at the south end, with stone steps leading down.

The outbuilding to the north is two storeys high on the north side and west end, with one storey facing south and east, built over the vaults. It is constructed of rubble stone with a slate roof and a high rubble stack on the east side. A small projecting structure at the northeast angle incorporates a gargoyle. The north side includes a door leading to the vault and a window above. The west front has a window above and a large flight of external steps providing access to a footpath between the building and the house. A cartshed is located beneath the footpath. The lower part of the outbuilding remains uninspected and potentially is vaulted.

Attached to the northwest angle of the outbuilding is a large stone, Tudor-arched gateway to a yard, possibly dating from the early 19th century, featuring an inner rebate for doors. It sits on the site of a College gateway marked on a 1720 map, and has an inner segmental arch. A thinner, lower wall extends beyond the gateway to the river bank at Cloister Bridge.

Behind the house are extensive remains of undercrofts relating to the crosswing, west wing and service wing of the college. These are enclosed by high rubble stone walls, supporting a grassed terrace with vaulted undercrofts beneath the crosswing, and with external steps leading up. The undercrofts of the west wing and the range running towards the river are currently inaccessible. The undercrofts are designated as a Scheduled Ancient Monument (Pe 445).