The picture you see is of a family crest made entirely of human bones, and each bone in the entire body is represented at least once.. There are actually something like 40,000 bodies worth of bones in this ossuary, and the place is full of bone art, including a chandelier made of skulls.
A chandelier made of skulls? Dudes, if that isn't metal, I don't know what is. I can literally envision Ronnie James Dio singing "Man on a silver mountain" in this church. Not only would it be awesome, but it would make complete sense. Can you imagine a better location for a Slayer video? Me either! I suppose it might be a little disrespectful to the dead, but then again, they have already been formed into various sculptures, so what difference will a little "Seasons of the Abyss" make?
Besides the metalness of this ossuary, I would also point out that the Czech Republic itself is pretty metal. Lots of dark old growth forests, werewolf stories and the bones of the Roman Legions laying around. The place practically screams for some band like Iced Earth to come and play a massive show, which they actually do fairly regularly since the Czechs love melodic power metal. If you play melodic metal and can sing in a high voice, you need to get to the Czech Republic, where they eat that stuff up.