66, St Mary Street

66 St Mary Street is a school building dating from 1733. It features a painted limestone ashlar facade, a rubblestone rear with freestone quoins, and a double-pitch plain tile roof with moulded ashlar stacks and stone coping at the gable ends. The building has a double-depth plan and is two storeys tall with a cellar, presenting a symmetrical five-window range.

The exterior includes a continuous moulded cornice with a small pediment above the central range, a deep moulded ground-floor string course, and 6/6-pane sash windows flanking a six-panel door that is glazed at the top with raised and fielded panels below, all sheltered by a moulded hood on brackets. There are also two 20th-century roof lights. At the rear, the windows feature stone mullions with semicircular arches and four 19th-century panes in each light, with some having sashes; there is a three-light window to the left and two-light windows in the center and right. The first-floor windows have ashlar aprons that extend down to a string course, which is interrupted at the center by a stair window with a cornice. A two-light basement stair window has flat arches.

Inside, there is a closed-string dogleg staircase with turned balusters, and the stone-flagged cellar is barrel-vaulted. The double-pitched roof is supported by collar trusses.