The brave souls inhabiting Miyakejima, one of Japan's Izu Islands, an archipelago just south of Tokyo, have a unique problem.
Here, the land rests atop an active volcanic chain that has erupted six times in the last century. However, the danger isn't just from volcanic eruptions, but from the highest concentrations of poisonous gasses (primarily sulfur) in the world regularly leaking up through the ground.
In 2000, a mass evacuation was instituted due to extremely high levels of toxic gas in the area after a series of eruptions from Mount Oyama, the main volcano on the island. All flights into the area were stopped for over eight years due to the high levels of sulphur as well. Miyakejima residents were finally permitted to return to their “normal” routines in 2005 though residents are required to carry a gas mask with them at all times.
Hypothetically speaking, were one to visit the Izu Islands, they might wake to a siren in the middle of the night, only to be met in the dark by a confused, wandering child wearing a gas mask, a hand extended asking "Are you my mother?"
Although Miyakejima appears frightening and almost post-apocalyptic, tourists can, in fact, visit the island. Aside from the dangers of poisonous gas, parts of the island are extremely lush and apparently the scuba diving is a beautiful experience filled with dolphin sightings. For visitors who believe the benefits outweigh the danger, gas masks are available upon arrival at many tourist shops on the island.