A bunker is a defensive warfare fortification of any sort to protect oneself. Bunkers are mostly below the Earth's ground level. They were used extensively in World War I and World War II. In the 1950s, the bunker became part of Americana culture. A famous bunker is the North American Aerospace Defense Command (NORAD). Some installations are giant underground complexes. The Soviet Union maintained huge bunkers during the Cold War. In Albania, the paranoid communist dictatorship of Enver Hoxha littered the small country with 500,000 - 700,000 bunkers.
Another type of bunkers is a little concrete post, partly dug into the ground, which is usually a part of a trenches system. Such bunkers are ment to give the defending soldiers better protection than the open trench and also include top protection against aerial attack (grenades, mortar's shells). The front bunker of a trench system usually include machine guns or mortars and form a domainant shooting post. The Rear bunkers are usually used as a command post, storage and field hospital to attend wounded soldiers.
Dug-in guard posts (with shooting slights) made from concrete are also known as pillbox. Some of the pillboxes have camouflage in order to provide the guards better protection and the element of surprise.
Typical industrial bunkers include mining sites, food storage areas, dump for materials, and sometimes living quarters.