Welcome to tourism on the beautiful Japanese island of Miyake-jima, due southeast of the main island of Honshu, where every person on the island is legally required to carry a gas mask with them at all times (Wikipedia). The island is home to 3,000 permanent residents that live on the barely-above-sea-level active volcanic cone seen here:
That active cone constantly pours down sulfur gas on the island, some days more than others. When the siren goes on after a sensor is triggered for too much sulfur ppm, everybody puts on their masks or risks suffocation. Continuous eruptions from 2000-2005 had the island completely evacuated by the Japanese goverment due to gas levels, but former residents moved back en masse when allowed to.
The gas-resultant strange flora/fauna and culture of the island make it a popular item for "gas mask tourism". At this point you may be asking yourself "Hey, isn't sulfur that horrible-smelling gas that makes the stinkiest of farts smell like rotten eggs?" Yes, yes it is. I guess you'd probably get used to it after a while when you lived there, but I'd imagine not during a short tourist stay.
In addition to a strange form of tourism, the island is also famous for some amazing historical pictures that are floating around, the best and most famous being this picture of a WW1-era wedding that took place on a gas mask day:
Happy Hamsterdam, all.