Bunkers were developed during the 19th century as a kind of fortress often separated from main strongpoints. They were built where the main offensive was expected, but due to high cost or natural conditions made building the whole fortress impossible. They could be used as defense strongpoints, but also can protect the headquarters from air or artillery attacks.
Six men that survived the ambush now try to find the refuge in isolated bunker. Inside they find two frightened soldiers and doors that lead to underground tunnels.
War films are not always showing the war per se - often the main theme is the influence of the conflict on lives of people involved, but also their families and friends. War is seldom a local thing - the trauma, the pain, the death they put their mark on people from around the world.