Fiery Cavern is Hell?

[CM30]

And by that, I mean literally. For one thing, the whole concept seems to be based on the concept of 'when hell freezes over', or something unlikely happens. In the case of the level, I guess hitting the switch and literally freezing hell is an unlikely concept...

What's more, it kind of explains why there's this random fire level in the middle of a horror themed world. I mean, hell is a scary place after all, and it's a nice favourite for various movies and games with creepy enemies and such (like Doom I guess).

So yeah, mystery solved I guess. Someone sure liked sneaking non Nintendo friendly themes and things into this game...

 

[ChanceTime]

I think it's probably what they were going for, given that, as you say, it's in the Sapphire Passage.

 

[Just a Wario Fan]

Given Fiery Cavern's placement in the Sapphire Passage and its theme, it seems to be based on Hell from Christian mythology. The way the level freezes over when Wario hits the Frog Switch is a reference to the term 'Hell Freezes Over', aka something very unlikely happens (such as a fiery place immediately being frozen).

This is what they say about Fiery Cavern on Mario Wiki. So yes, it really is hell.