Castellated structure to NW of The Sluice

Tall square structure of rubble stone, square plan, with castellated parapet and tooled stone quoins. E elevation facing The Sluice has high wide arched recess to left, and arched doorway to right with double doors. Tiny lunette light to left of recess, lighting a mural stair. Both the giant recess and the doorway have tooled stone voussoirs with keystones and are slightly set back in square-headed frames. Within recess is cobbled floor, cemented seat and arched door to left to stair witihin the wall. Stone voussoirs to arch. N elevation to Duke of York's Wharf has 2 tall blocked round-headed arches (the ends of the vaults within) with keystones, stone pier between and impost band. Three small square blank openings in spandrels and date stone of 1848 between arches. Infill of each arch has 2 windows with timber lintels.

Two large stone-vaulted chambers.