Underwater stuff (only done minimally in FFXI in the undersea ruins- but you wouldn't really know you're underwater if you didn't visit one of the few rooms that actually have windows)By underwater I mean like you get a special aqualung item or whatever and you're actually walking on the lake/oecan floor.

Also hot lava zones. much more hot lava-y than places like Ifrit's Caldron from FFXI. I mean very lava-y and hot like magmoor caverns in metroid prime or lethal lava land in super mario 64.