In the Alsace region of France, road builders have discovered a trenchwork from WWI perfectly preserved due to a hit from a gigantic shell that collapsed the trench onto the soldiers inside. 

In the picture below can be seen beds, a bottle and a helmet.

                      The scope of the trench is extensive, as can be seen from this aerial view.

                      21 German soldiers were found entombed inside, one still laying on his bed.

Below is a contemporary photograph of a similar trench, and gives an idea of how many people were in there.