"Underground" is a 1995 award-winning film directed by Emir Kusturica.
It is also known by the subtitle Once Upon a Time There Was a Country.

It's the story about an underground weapons manufacturer in Belgrade during WWII and evolves into fairly surreal situations.
A black marketeer who smuggles the weapons to partisans doesn't mention to the workers that the war is over, and they keep producing.
Years later, they break out of their underground "shelter" - only to convince themselves that the war is still going on.
Underground's soundtrack was composed by Goran Bregovic. Several songs from the album "Underground " such as "Mesecina" and "Kalasnjikov", became instant-classic tavern and brass-band hits.