If were running low fantasy, it is also very likely the whole chernobyl thing could develop organically. Awful continually deadly thing happens at point X (can be the result of hubris or mismanagement or whatever). Communication travels mostly at foot/horse pace, so the first anyone hears of this thing maybe a guy mumbling a few words as he staggers into town and dies (after feeding the dramatic plot points needed).... and then they have to figure out how to get close enough to do a thing.
Maybe knights can get in closer because the metal protects them from "the curse". Maybe the wizards did it and they don't want their name sullied. IDK, but I would play in it in a heartbeat.