Well, a lot of ideas came to mind. Zelda dark world ideas of course, but then I thought of stargate SG-1, and my choice became clear.  Might be a bit too ambitious, but I think I can pull something off with very simple graphics.

Basic Idea is this: A meteorite crashes into your planet. You investigate to find that it was really some sort of portal. You bravely step through it and find yourself on an alien world.

Modeled and UV mapped a simplistic human model that I can throw on some quick textures to have different looking humanoids.