I'm sure that every military has its share of cave complexes built into solid rock. My mandatory service in the Finnish Defense Forces took me to 5 such places,

I'm sure that every military has its share of cave complexes built into solid rock. My mandatory service in the Finnish Defense Forces took me to 5 such places, of which at least 3 had multiple levels (I can't say for sure how large any of those were, because they were generally of limits to conscripts; I was only in them because my tasks (mostly installing fiber optics and such) required it).