Interesting. Im quite sure Tartarus is related to the Tatry mountain range i.e. the land behind Tatry is the Tartarus. land of the dead. One of the most famous legends here is that of the sleeping knights under the Tatras , who are supposed to wake up for the final battle. Anyway, that video is titled "the crypt of Slavic kings", but to be honest nobody knows what this place really is and even more. nobody wants to investigate it. The guy from the video was the most prominent Polish prepper and he died in rather strange circumstances after being harrassed by the police. Oh and these crypts is located right under one of the most sacred mountains in Poland.