Including Gatepiers, Atrium House (Former Gardener's Cottage), Callendar House, Callendar Park

This late 18th century building is a single-storey, three-bay former gardener's cottage that has been converted into an office in the mid-1990s. It is located within the former walled garden of the Callendar Estate, on sloping ground to the north. The structure features extensive alterations and additions to the rear from the late 20th century. It is constructed of random and squared rubble with raised ashlar dressings, stone cills, strip quoins, droved rybats, rubble tabs, and stone skews. The eaves course is simple, banded, and corniced, with a blocking course that conceals the rainwater goods.

On the principal (south) elevation, there is a central, shallow Doric entrance portico supported by a pair of plain shafted columns, which hold up a plain rectangular entablature with a banded cornice and blocking course. Flanking this portico are windows. The east elevation presents a plain gable, while a later single-storey rectangular-plan extension from the 1990s adjoins the cottage on the right, incorporating the original boundary wall. The north (rear) elevation features an extensive addition from the 1990s that advances to the left, with the original bay set back to the right. The west elevation includes a window in the central gablehead, with a boundary wall adjoining to the far left.

Inside, the building has been converted to office accommodation in the late 20th century. It contains 12-pane timber sash and case windows and three cast-iron roof lights from the 20th century. The pitched roof is covered with grey slates and features lead ridge and eaves lining, straight ashlar skews, and coped ashlar stacks with small thackstanes and circular clay cans.

The gatepiers consist of two tall, chamfered, square-plan ashlar structures with splayed bases and corniced caps. A stone lintel connects the right-hand pier to the west gable of the cottage, forming a side gateway. There are late 20th century cast-iron gates at both openings.