Zone Rouge in France.
An area originally 460 square miles in northern France so toxic after WWI that not only were towns not rebuilt.
The area is saturated with unexploded shells (including many gas shells), grenades, and rusty ammunition. Soils were heavily polluted by lead, mercury, chlorine, arsenic, various dangerous gases, acids, and human and animal remains.[1] The area was also littered with ammunition depots and chemical plants.