This type of bunker is a small concrete structure, partly dug into the ground, which is usually a part of a trench system. Such bunkers give the defending soldiers better protection than the open trench and also include top protection against aerial attack. They also provide shelter against the weather. Some bunkers may have partially open tops to allow weapons to be discharged with the muzzle pointing upwards (e.g., mortars and anti-aircraft weapons).
Many artillery installations, especially for coastal artillery, have historically been protected by extensive bunker systems. These usually housed the crews serving the weapons, protected the ammunition against counter-battery fire, and in numerous examples also protected the guns themselves, though this was usually a trade-off reducing their fields of fire. Artillery bunkers are some of the largest individual pre-Cold War bunkers. The walls of the 'Batterie Todt' gun installation in northern France were up to 3.5 metres (11 ft) thick, and an underground bunker was constructed for the V-3 cannon.
Typical industrial bunkers include mining sites, food storage areas, dumps for materials, data storage, and sometimes living quarters. They were built mainly by nations like Germany during World War II to protect important industries from aerial bombardment. Industrial bunkers are also built for control rooms of dangerous activities, such as tests of rocket engines or explosive experiments. They are also built in order to perform dangerous experiments in them or to store radioactive or explosive goods. Such bunkers also exist on non-military facilities.
When a house is purpose-built with a bunker, the normal location is a reinforced below-ground bathroom with large cabinets. One common design approach uses fibre-reinforced plastic shells. Compressive protection may be provided by inexpensive earth arching. The overburden is designed to shield from radiation. To prevent the shelter from floating to the surface in high groundwater, some designs have a skirt held down with the overburden. It may also serve the purpose of a safe room.

Large bunkers are often bought by super rich individuals in case of political instability, and usually store or access large amounts of energy for use. They are sometimes refereed to as "luxury bunkers," and their locations are often documented.
Munitions storage bunkers are designed to securely store explosive ordnance and contain any internal explosions. The most common configuration for high explosives storage is the igloo shaped bunker. They are often built into a hillside in order to provide additional containment mass.

A specialized version of the munitions bunker called a Gravel Gertie is designed to contain radioactive debris from an explosive accident while assembling or disassembling nuclear warheads. They are installed at all facilities in the United States and United Kingdom which do warhead assembly and disassembly, the largest being the Pantex plant in Amarillo, Texas, which has 12 Gravel Gerties.

• 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
• Object 17/5001 Prenden, Germany
• Bunker of the Harparskog Line in Raseborg, Finland
• Beach bunker with improvised art in Blåvand, Denmark
• Bunker in Singapore
• The entrance to Ouvrage Schoenenbourg along the Maginot Line in France.
• Bunkers in Albania
• German single person bunker for reconnaissance personnel in the field
• Bunker of type Winkel in Brandenburg an der Havel
• Munitions bunker at Possum Park, Queensland, Australia.
• Gravel Gertie at the Pantex nuclear weapons plant, Amarillo, Texas.
• Austrian bunker from World War I in West Ukraine
Bunkers deflect the blast wave from nearby explosions to prevent ear and internal injuries to people sheltering in the bunker. While frame buildings collapse from as little as 21 kPa (3 psi; 0.21 bar) of overpressure, bunkers are regularly constructed to survive over 1,000 kPa (150 psi; 10 bar). This substantially decreases the likelihood that a bomb (other than a bunker buster) can harm the structure.

The basic plan is to provide a structure that is very strong in physical compression. The most common purpose-built structure is a buried, steel reinforced concrete vault or arch. Most expedient blast shelters are civil engineering structures that contain large, buried tubes or pipes such as sewage or rapid transit tunnels. Improvised purpose-built blast shelters normally use earthen arches or vaults. To form these, a narrow, 1–2-metre (3.5–6.5 ft), flexible tent of thin wood is placed in a deep trench, and then covered with cloth or plastic, and then covered with 1–2 m (3.5–6.5 feet) of tamped earth.

A large ground shock can move the walls of a bunker several centimeters in a few milliseconds. Bunkers designed for large ground shocks must have sprung internal buildings to protect inhabitants from the walls and floors.
Nuclear bunkers must also cope with the underpressure that lasts for several seconds after the shock wave passes, and block radiation. Usually, these features are easy to provide. The ov…

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Bunkers can be destroyed with powerful explosives and bunkerbusting warheads. The crew of a pillbox can be killed with flamethrowers. Complex, well-built and well-protected fortifications are often vulnerable to attacks on access points. If the exits to the surface can be closed off, those manning the facility can be trapped. The fortification can then be bypassed.