[HoneyBadger]

Thank you Uninspired Name, and thank you Cainehill, for the physics lesson. Always nice to learn something new. Anyway...my intention for extreme water and fire realms wasn't that they be enormously useful, compared to caverns. There's a reason people used to live in caves, and that's because caves a great places to live, especially when one of your options is to live inside a smilodon's belly. I'd want these realms in the game to add flavor, to maybe provide a handful of unique provinces here and there. Creatures, magic items, pretenders, and heroes could come from them, maybe go there, but in general, very few are going to want to move there, or even could. It would be the fact that they existed in the game, and the sense of wonder from that (ever wonder about outer space?) that I think would only add to the game's "romance" as it were. Also, my opinion is that it wouldn't be difficult to code them in, which is always a plus, and once they're in, certainly some use can be wrung from them.

As far as cloud realms or heavenly realms, well why not?
Considering that quite a few creatures fly and spells can compensate for those that lack (and why not spells to access and explore extreme depths or extreme heat/cold? and why not the realms of the Rimsurtar while I'm riding on this mad train?).

My whole point is that I'm glad cave provinces are in, and I hope to see different areas also opened up, even if I can't stick a castle or a flag on it and call it home.