Intramural galleries, passageways created in hollowed out sections of the surrounding curtain wall, were a feature of later medieval castles, allowing the rapid movement of defending soldiers between arrow loops where they could fire down on attacking troops. Several castles had their basement areas pressed into service as air raid shelters during the Second World War, though the use of intramural galleries appears to have been unprecedented. The story at Cardiff is not clear cut however as the intramural galleries may have been completely an invention of the 3rd Marquess of Bute, formed during late 19th century remodelling and reconstruction works in order that he could take sheltered walks in wet weather.
All the same, the City Engineer saw their potential and in May 1939 asked the new Marquess, his son, for permission to use them as public air raid shelters, a courtesy since he had the power to press them into service. By October 1939 works were in progress and the respite of the Phoney War allowed work to go ahead in conditions of relative calm. The galleries were subdivided by blast walls into eight linear sections, each of which could accommodate over a couple of hundred people, while to cut down on the travel distances that could be a matter of life and death in a raid, four new entrances had to be formed on the city-facing side of the walls, each feeding into a pair of compartments via external timber ramps.
The “Castle Wall Shelters”, as they became known, could accommodate up to 1800 people in total and were considered among the safest in the city thanks to their thick stone external walls, reinforced by a banked earth rampart on the inside. They became so popular that local shops would advertise how close to the castle shelters they were in order to attract in nervous customers. Contemporary accounts refer to “dormitories with bunks, kitchens, toilets and first aid posts concealed within the walls” recalling the period from March 1941 to May 1942 when the shelters were designated as dormitory shelters.
Shelter use ceased on December 1944 and shortly after the war the ramps were removed and the external wall openings sealed up. Following the death of the 4th Marquess in 1947 the castle came into the hands of the City Council and was opened to the public, though the shelters remained closed until 2011.
For further details on visiting refer to Cardiff Castle.