A passage from the eastern side of the terreplein descends to a rectangular lobby, the southern part of which was an expense magazine in 1881, though no evidence of this remains. From the lobby, the gallery leads through four casemates to both north and south of the lobby. The casemates are mainly of brick laid to English bond, with axial vaults of stretchers and the rear walls are of chalk ashlar. In 1867, in order to arrest movement of the gallery, an additional battered wall was been built against the exterior of the vertical scarp revetment, thus sealing the loopholes and rendering them useless. (location accurate to the nearest 1m based on available information)