A bunker is a defensive military fortification designed to protect people and valued materials from falling bombs, artillery, or other attacks. Bunkers are almost always underground, in contrast to blockhouses which are mostly above ground. They were used extensively in World War I, World War II, and the Cold War for weapons facilities, command and control centers, and storage facilities. Bunkers can also be used as protection from tornadoes.
The Flakturm at the Augarten in Vienna. Flak towers were used as both above-ground bunkers and anti-aircraft gun blockhouses by Nazi Germany
The north entrance to the Cheyenne Mountain Complex in Colorado, United States
Inside the Hill 60 Bunker, Port Kembla, New South Wales, Australia. One of many bunkers south of Sydney
In a Project 131 tunnel under the hills of Hubei
A blockhouse is a small fortification, usually consisting of one or more rooms with loopholes, allowing its defenders to fire in various directions. It is usually an isolated fort in the form of a single building, serving as a defensive strong point against any enemy that does not possess siege equipment or, in modern times, artillery, air force or cruise missiles. A fortification intended to resist these weapons is more likely to qualify as a fortress or a redoubt, or in modern times, be an underground bunker. However, a blockhouse may also refer to a room within a larger fortification, usually a battery or redoubt.
Completed in 1750, Fort Edward in Nova Scotia, Canada is the oldest remaining military blockhouse in North America.
Reconstructed European wooden keep at Saint-Sylvain-d'Anjou, France, has a strong resemblance to a North American western frontier log blockhouse
The Henrican blockhouse at Mount Edgcumbe near Plymouth, Devon, which is believed to date from circa 1545
Blockhouse of Westreme Battery, built in 1715–16 in Mellieħa, Malta
