|There's a preview of Horizons: Empires of Istaria at The Junkyard. While there has been little new info about this MMORPG around lately, the article sums up known things pretty well (although you can't tell if much if that will change in the near future - they seem to change a lot of game elements right now). Here's a bit from the preview:
Players will be able to traverse the surface via mounts, caravans, ships (and walking of course). In addition to just seeing the surface, gamers will be able to explore underground caves and dungeons, as well as underwater areas of the map.
Much like the real world, climates will be different based on where you are on the map. Travel north into the snowy regions of the Ber'rak Glaciers, it gets cold. If your race is used to a warm climate, better be sure to bring clothing along to keep you warm. You could freeze to death. Travel into a desert, bring plenty of water with you. Don't carry too much though, your backpack is based on weight and volume, not empty slots.