My game world, as I’ve mentioned before, is very heavily based in the forests and hills of England, Germany, and New England. In much the same way that most of the planets that SG-1 visits looks like the Pacific Northwest, my world looks like temperate forests. Does my world have jungles and deserts and badlands? Absolutely! Does anything ever happen there? Probably, but I’ve never worried about it.
In my PbP game, one of the characters is playing a rather savage elf from the jungle. Suddenly, my Megadungeon (the game’s setting) moved from under the ruins of a hillside castle, to under the ruins of a jungle temple. Just as suddenly, I'm exploring a part of my world that I hadn't ever visited.
All because of one choice, a choice I wouldn't have made, a choice that I didn't make, my world has changed. I'm now forced to confront something that I hadn't before. My world has literally changed because of this one choice.
Now I'm considering that my megadungeon may distort space, and that entrances thousands of miles apart may all connect to the same dungeon... I may need multiple first levels...