That was litteraly my first thought when thinking about it. But as i stated in the original post, a cave would represent a greater element of the game, though a snow biome still a great idea
Id make a mountain and have the enterance 20 block high or somthing, then just do the cave in there. I am considering somthing clawing out of the ground, really like that.
Make a small tower. There's one element of Minecraft which transcends all 3 worlds; player construction.