Fort Erie's powder magazine. Unusual in that it's integrated into the barracks' basement, whereas in my experience a starfort's powder magazine has generally been a freestanding structure, the better to prevent cataclysm if it blows up...but just such a cataclysm occurred in September of 1814, during one of the British attempts to retake the fort by storm. A powder magazine exploded in the fracas, instantly killing 300 British troops. Assumedly that's why Fort Erie's powder magazine is where it is today: A previous, detached one was what exploded in 1814.