The unusual-shaped bunkers on the south-east outskirts of Calais are a series of First World War troop shelters with ornate brick arches inside and a concrete outer shell.
These were repurposed by the occupying German army from early 1940 onwards and several were adapted to provide a small amount of defence to the troops who used them as their barracks.
One has the addition of a stand for a 5cm KwK anti-tank gun plus there’s also a Tobruk built to house a captured French tank turret nearby.