Higashi Onsen

The ferry Mishima departs from Kagoshima Port three times a week and takes three and a half hours to cross to Iojima, which gives you time to watch the city skyline diminish and the open East China Sea expand around you. When the island comes into view, it announces itself with a pale column of volcanic gas rising from the summit of Mount Iodake, which is still actively venting sulfur above the treeline. The island has about 130 permanent residents, a small harbor, and a single paved road. Higashi Onsen is at the southern end of that road, on a shelf of black lava rock where the ocean is loud and constant.

There is no building here, no entry booth, no locker room. Three stone pools of different sizes sit directly on the lava shelf, open to the air and accessible at any hour without charge. The water that fills them comes from a highly acidic volcanic source measuring pH 1.5, which places it among the most acidic springs in Japan. The mineral content is dominated by alum and sulfur compounds, and the combination turns the water a distinctive pale green from colonies of thermophilic cyanobacteria living in the hot, acid environment. Sulfur clouds drift overhead from the mountain, and the ocean spray reaches the outermost pool when the swell is running. Soaking in water this acidic produces a clean, sharp sensation on skin, not unpleasant but distinctly chemical, and a faint white residue forms on the rocks at the pool's edge where the water evaporates.

Iojima's wildlife is unmistakable. Sea turtles come ashore on the island's beaches in summer to lay eggs, and wild peacocks, introduced when a resort was being developed in the 1970s and never contained, now roam freely across the lava fields and the village roads. Watching a peacock pick its way between the volcanic rocks toward the sea while you sit in green acid water under a sulfur cloud is an experience that does not fit into any existing category of travel writing.

Because the ferry runs only three times weekly and the island has minimal accommodation, most visitors plan a stay of at least one night. The pools are busy during the two hours after the ferry arrives and quiet at all other times. Going at dawn or late evening, when the acid water catches the light differently and the mountain above is steaming against a clear sky, is worth the disrupted schedule. Higashi Onsen appears on Japan's list of Top 100 Hot Springs, which is how most people first hear about it, and it is one of the rare entries on that list where the reality exceeds the description.