Russia
Despite what you may think, this landform is not the same as California's Death Valley. Not content to let America have all the fun, Russia has its own Valley of Death at the Valley of Geysers in the Kamchatka Peninsula that's arguably deadlier than its American counterpart. However, the danger here lies in the toxic gas released by the volcano — it’s killed all plant and animal life in the valley, and humans notice adverse symptoms immediately upon entering the area.
The mile area at the foot of the stratovolcano Kikhpinych is the "Valley of Death" itself where volcanic gases kill anything that enters. In the late 1900s, researchers determined that the trap is created by a toxic mix of hydrogen sulfide, carbon and sulfur dioxide, and carbon disulfide. You don't have to be a chemist to realize that it isn't a friendly mix...