How do I get off the mountain? And how do I get to the cross?

I'm sorry. I've played both Dark Sun games and neither have anything like what you're describing. The Dark Sun games don't use paladins all that much anyway. Are you sure you posted in the right forum?

Paladins aren't a playable class in the Dark Sun games, so yeah, maybe the OP is confused with another game or misposted?

Yes. That's what I meant by "not using paladins all that much." You can't play them in this series. There is one undead paladin NPC in the first Dark Sun game, who can grant access to a miraculous healing chamber, provided you uphold her values, but that's about it.