Catacombs of Jajce
Walled city of Jajce, Bosnia and Herzegovina
The Jajce Catacombs, also known as the Jajce underground church, or simply Jajce crypt in Jajce, Bosnia and Herzegovina, is the historic burial site of Hrvoje Vukčić, a Bosnian nobleman who founded the city and ordered construction of the underground chapel with the crypt around 1400, which was finished before 1416, in time for his burial. The crypt was also meant to serve as the family's burial site.
Cemetery data from Wikidata (CC0). Summary from Wikipedia (CC BY-SA).