Attached is a French photograph from 1915 showing the entryway to one of the many subterranean shelters that dotted the Western front during the First World War; also shown is a diagram illustrating one of the smaller German dugouts with a similar entrance. Unlike the Allies (who always liked to believe that they were going to leave their trenches any minute and march on to Germany), the German trenches tended to be far more comfortable - better walk-ways, smarter dugouts, tidier latrines. There were some reinforced with bricks or concrete, with electric lighting.
Click here to read an article about life in a W.W. I German listening post...