A hex zone is a place heavily marred by dark magics.
In the most heavily corrupted zones are covered in a dark haze, which causes lingering spirits and feelings of anger and despair to physically manifest as strange ethereal monsters. The shape and nature of these spirits his highly unpredictable, and they are capable of reshaping, animating & possessing the landscape.
The atmosphere in hex zones is not safe for unprotected people to navigate.
It is possible to remove hex zones, and clean-up crews have been organized to fix them. Navigating a raw hex zone is dangerous work requiring significant training and protective gear. The cleaning process is equal parts manual labor and ritual and can take months to years.