Bulgaria was lacking an artistic tradition in cinema before the communist era and during this era the party line was more important than free artistic expression. Most movies were made to satisfy the domestic taste or as propaganda. The Goat Horn (Kozijat rog) from 1972 is an exception and a gem.
It is a minimalist story about revenge, taking place in the Bulgarian lands of the Ottoman Empire during 17th century. Black and white, scarcely any dialogue and no music, except for a song whose words are never sung but just hummed and with its grittiness and naturalistic acting it is reminiscent of the Italian neorealism or, being a history piece, to an early Kurosawa film.
If it were made 10-15 years earlier, could have been a landmark movie in world cinema, despite some technical limitations (sound was poorly added in post-production) and in few parts somewhat clunky narrative.