The World At Large
A land burned by magic.
The reason how or why this happend has yet to be discovered. The land also has been regarded as uninhabitable by all but the strongest-willed person.
The conditions inside The Corruption are random at best. In fact, random is not a strong enough word. The land is temperamental, deciding that it does not like that 2+2 = 4 and changes it to 2+2 = gh23%. It will also enjoy a upside-down tornado in a blizzard from time-to-time, maybe.
Basically, it completely ignores the going-ons and rules in the outside world and lashes out as it sees fit. Though not always in a terrible and horrific way. If you are lucky it will only be puzzling, in a brain-melting way.