Thorne Island Fort

Thorne Island Fort is a 19th-century military battery situated on the highest ground to the west, behind a low parapet. At the rear, there is a parade ground approximately 5 meters below the battery level, surrounded to the north, east, and south by vaulted single-storey barracks and ancillary buildings. Beneath the parade ground, there are water reservoirs with a capacity of 30,000 gallons.

The northern range includes a cookhouse and officers' quarters, while the eastern range contains barracks for other ranks, with the entrance to the fort and guardroom located at the center, occupying a small bastion. The southern range features additional officers' quarters, and at the western end of this range, there is an armoury protected by a solid half-round bastion extending from the exterior wall. The barracks ranges showcase fine brickwork groin vaulting.

These barracks have flat roofs with access to parapets facing east and south, which include apertures for small arms fire. A bridge connects the southern and eastern ranges. The fort is constructed from limestone ashlar masonry, characterized by prominent quoins and a large shallow string course at the base of the parapet. The entrance on the east features a voussoir arch with a projecting keystone and lettering, flanked by side pilasters with simple cornices. The reinforced outer entrance doors are approximately 12 centimeters thick and operate on a floor track, while the inner entrance doors are missing and also ran on a floor track.

The front of the barracks ranges facing the parade ground is made of hammer-faced ashlar, with a large shallow squared cornice and quarter-round moulding beneath. Six-pane sash windows are present, and granite staircases lead up to the battery.