Therion

Apparently these Swedish guys are very popular here and that's why they are returning for another concert.
I don't listen to any heavy metal, but these graphics grabbed my eye today (because of the Theta-connection). A quick search reveals that they were inspired by Nordic mythology, and this has become entirely Christopher Johnsson's project, who is into a type of "dark and confused spiritual realm, which he completely owns up to, however". Good on him.

I don't see this going any further with me, but I'll just do a quick research as an exercise. I do know most of those references. And no, it may be dark but it isn't necessarily confused (one's own judgment of it can be), and the lyrics are not "difficult to penetrate" - they're straightforward listings of occultist concepts. When I say occultist concepts, I mean "the way the occultist inteprets that which is". (The suffix "ism" means that you commit yourself to a particular way of seeing and interpreting information. However, the same reality may be encountered by other groups, who will present it in a different light).