Chapel

The building is a prison chapel, formerly used as an Officers' Mess, constructed around 1865. It is possibly designed by Captain W. Crossman, Royal Engineers, who was the general designer for The Citadel. The chapel is made of Portland stone with roach stone rustication and has a slate roof. It is a long, narrow structure oriented east to west.

On the south side, there is a central porte-cochere featuring segmental-headed double doors and arched openings, with two windows to the south and one each to the east and west, all of which are 20th-century steel casements. The building has a modillion cornice and a blocking course. The rear of the building is plain and has undergone some repairs due to wartime bomb damage. There are three eaves stacks with cappings.

Inside, the chapel has been significantly modified but still retains a three-arched screen supported by paired columns at the east end. The architectural detail is consistent with that of Officers' Block B. It appears that a U-plan block was originally intended, as indicated by the remaining foundation walls to the north, but there is no evidence that this plan was ever fully realized.