Cool.
Usually, they discover thousands of pounds of un-exploded ordnance.
And not in a good way, at times. :^) One of my old teachers did cold war intel work in Europe (nothing too lofty) and he and his buds had their favorite bars. Their usual place was owned by a former German soldier who described his experience trying to dig a basement. The backhoe brought up an unexploded bomb. Uh, he shut down the machine and called the bomb squad. Oh, and kissed his backhoe goodbye. :^)