Horseshoe Bastion, which is located on the north eastern side of the Castle and forms part of the outer defences, was constructed between 1794 and 1805 as part of a vast programme of works to remodel the Castles defences and is one of four new bastions constructed in this period. The bastion was provided with a long covered access tunnel that extends beneath the ramparts and allows access from within the castle.

The bastion is a very large embanked structure constructed from the chalk which was quarried from the ditch with a horseshoe plan. Within the counterscarp bank to the rear of Horseshoe Bastion is a rectangular plan three-bay vaulted brick chamber which provided shelter for the garrison here. There is a doorway which allowed access to the east ditch by means of a small draw bridge and there is a tunnel which leads from the chamber to the south east corner of the bastion. The long tunnel from within the castle has chalk walls and is brick vaulted. The apparent lack of a firing step or gun embrasures suggests that the bastions may have been designed for a heavy mortar.
. Summarised from sources (1-2)

<1> English Heritage, 2014, Dover Castle Conservation Management Plan Volume 2 Gazetteer (Unpublished document). SKE52105.

<2> Johnathan Coad, 1995, English Heritage Book of Dover Castle and the Defences of Dover (Monograph). SKE52106.