Avari
Four Thousand Club
Oh hell yeah, this is late game stuff for sure. The Ashen Mountains is probably at the level of the Deluge Wetlands for survivability, if not worse. That'll take a long time to work up to, but it'd be an awesome late game.
Granted we'll all probably die, but it'll still be a good time xP
Ashen Mountains isn't as dangerous I think. The danger comes from the potential of sparking another war if anyone gets caught stepping foot on it.