Grenville Battery

Grenville Battery is a fort built in the late 18th century, with some additions from the 19th century and during the First World War. The structure features a limestone rubble basement and walls, with sandstone rubble at ground floor level, and bomb-proof stone roofs that were originally slated. The fort has a roughly triangular shape, with a long gatehouse and barrack rooms along the northeast side, which faces landward.

The gatehouse and barrack rooms are single storey, built on a battered basement. There is a central segmental-headed gateway with brick dressings, and loops along the base of the barrack rooms that face inward to defend the gate bridge moat. On the inner side, the barrack rooms have window and door openings with flat heads, keystones, and voussoirs, and the rooms feature vaulted brick ceilings.

The seaward sides have stone-paved ramparts that include three large reinforced concrete gun emplacements designed for very large sea-firing guns, along with ammunition hoists and crew shelters attached to these emplacements. Older gun emplacements can still be found on the west side. The ramparts are constructed of rubble, made from small blocks and laid in a rough manner.