Long before recorded history a cosmic disturbance caused [the world] to be moved from its normal place directly in the middle of the cosmology towards the Elemental Chaos and away from the Astral Sea. Since then corruption has spread from the corners of the world leaving only pockets of land unaffected: from the Griman Sea (black as pitch and birth place of many aquatic aberrations) to the Struck Wastes (a broad strip of dead land including both desert and tundra), extreme environments abound and even characters from the untainted lands must be made of iron to survive (of course, this is not limited to physical strength).
Despite many attempts by daredevil explorers, an accurate map has yet be drawn. [I promised this isn’t just because I’m lazy. While I am happy to come up with as many crazy environments as necessary, players are encouraged to invent wild areas of their own even if only so their own character can come from that place.]