A guardroom is a room for soldiers who are guarding a military camp. They wait there between patrols, keep their things there, and it is the place you go if you need the people on duty. Think of it as the guards’ room inside the camp, not the little building at the gate. A guardhouse is a building; a guardroom is a room, often inside a larger building. Though actually, in British army talk the guardroom has also been the place where a soldier is held for a short time if they are in trouble — so the word can feel a little like the army’s small lock-up. The meaning here, though, is the room for the soldiers doing the watching.

衛兵房