I Ate a Meal Cooked in a Stinky Hot Spring

A pack of shrieking Japanese macaques, endowed with red testicles and red faces, crossed the road in front of us, distracting us just enough to miss the last bus to our lodging in Yunomine Onsen. When we arrived, we were greeted with the stench of sulfur that rises out of Yunomine's hot spring, the onsen that made the place famous.

We had been trekking the Kumano Kodo, an ancient Buddhist pilgrimage route across central Japan's Wakayama Prefecture, and we were exhausted. After speed-hiking the first half of the Nakahechi route, trying to make up for the two days we lost to the over-hyped Typhoon Vongfong, our legs were weary. We hiked a mountainous 22.1 kilometers that day.

Yunomine Onsen, a one-street town that's built along a creek in rural Japan, is credited as the country's oldest spa. It may be the world's only UNESCO World Heritage Site you can soak in, and it's blessed with a 93 degree Celsius (202 degree Fahrenheit) public hot spring in the center of town that has been healing travelers' achy legs for 1,800 years.

Located just beyond Kumano Hongu Taisha—one of the holiest of the 99 shrines, or oji, that line the Kumano Kodo—Yunomine's hot springs were the sites of Japanese Buddhist ablution rituals, purification rites for pilgrims who traveled the arduous journey to visit the shrines. Towns were built along the Kumano Kodo to support the pilgrims, and the trails now weave in and out of rural villages like Yunomine.

The hot spring at Yunomine Onsen is the stuff of Japanese legend. The area was named after the town's main deity, the Healing Buddha. A Diary of Yunomine Hot Springs (1840) by Nagasawa Tomo'o identified the Healing Buddha as Yakushi Nyorai (yakushi means "medicine" and nyorai means "a person who has attained Buddhahood"). Legend has it that hot water sprang from the breast of the Yakushi at Toko-ji, a temple in the center of town dedicated to him. The name Yunomine may have sprung from here, too; historians assume the expression Yu-no-mune (literally "the breast of hot water") was corrupted into Yu-no-mine over the years.

Japan's location on the Ring of Fire has bestowed upon it over 3,000 natural hot springs, and in the eight days we spent in the Wakayama Prefecture, I took close to 25 baths. But Yunomine Onsen is the mother of them all—one of the oldest, smelliest, and most sacred of the storied springs—so I was counting down the minutes until I could take a dip in it. I just didn't expect that I'd be eating from it, too.

Just after sunset, Tamoko, the server at our ryokan, a traditional Japanese inn, covered our dinner table with dozens of small dishes. The first few were familiar: various types of pickled vegetables, yama-imo, river fish parts (e.g., raw, sliced red-spotted salmon head), and fu. She then poured a little cup of the sweetest booze-nectar I've ever had the pleasure of tasting. Tamoko told us it was onsen umeshu, a plum liqueur made in town using the stinky hot spring water.

She brought in a small hotpot that was filled to the brim with onsen water, along with a side of slippery, raw Mii-Kumano beef, marbled with fat, to cook shabu-shabu style. That's when Tamoko told us shabu-shabu is actually an onomatopoeia for the bubbling sound food makes when you drag it across the boiling water's surface.

Next was onsen tamago, or egg boiled in onsen water, which tasted mostly like egg, only eggier and slightly putrid, like it had been nestled in sweaty gym socks overnight. The magic was in the texture, a custard-like consistency imparted by water that is naturally near the boiling point and fortified with the minerals it collects on its way out of Earth's bedrock. The egg white never completely solidifies.

In the morning, we were served a similarly prepared egg alongside onsen rice porridge. Before we lifted the lid, Tamoko warned us, "Western people never touch the porridge." But I grew to love it, the way one grows to love stinky tofu or durian after a while. Once we removed the lid, the table reeked of sulfur. But we ate on, adding the egg and some umeboshi to the smelly goo.

As if the putrid smell weren't off-putting enough, the water yellows the food. The rice porridge is normally white-gray, but it now had a yellow tinge, courtesy of mineral content of the onsen water in which it was cooked.

According to the Kumano Hongu Tourist Association, Yunomine Onsen's water contains high concentrations of hydrogen sulfide, sodium, hydrogen carbonate, magnesium, and calcium, along with a dozen other minerals, which give the food a distinctively meaty flavor.

In the Tale of Oguri Hangan and Princess Terute, first told over 500 years ago and still told today in kabuki and religious narratives, the tsuboyu's mineral-rich waters cured Oguri from debilitating disease. Bathing is rumored to help with rheumatism, skin diseases, and diabetes. Drinking the water is even better.

The inns in town advertise these health benefits, believing that consuming the water is one step better for you than bathing in it. On the website for one of the town's guest homes, Minshuku Yamane, the meals are billed as handmade and "very good your health [sic]." Drinking from the hot spring is said to help with gastrointestinal ailments and gout.

Kind of grossed out (but mostly intrigued) that we bathed in the milky, smelly hot water from which we ate, we went down to the creek in our yukatas and slippers to see people cooking in the hot spring. The famous tsuboyu, a small hut that people can rent for 30-minute time slots to dip themselves in scalding water (literally so hot that you have to top it off with freezing water from a hose for close to 15 minutes so that you don't get burned) is not where people cook. People carry red net bags full of eggs to the Yuzutsu, the square hell pit in the center of town from which stinky steam rises. They cook there, at this hole in the ground, where the water bubbles up and replenishes itself from beneath the surface.

Chunks of white mineral deposits float in Yunomine's onsens. There are signs that try to ease bathers' concerns about the floating gunk: they say they're called Yu-no-hana, or hot spring flowers, and assure you that they're beneficial for your health. A sign on the Yuzutsu also says, "Don't steal the onsen eggs!" in Japanese.

Gaggles of tourists and locals alike gather around the box and tie their bags to a thin wooden plank on the side, letting the eggs sink below the surface. Some sneak off to soak themselves in the kusuri-yu (medicine water) while their eggs cook. Either way, within 12 to 15 minutes, the eggs are done. It's that hot.

People purchase their eggs and vegetables at one of the shops in town. The shops sell kits: a dozen or so eggs, netting, rope and salt. Some haul eggs and vegetables—bamboo shoots, spinach—from home to avoid the ¥200 (about $1.60) charge, but everyone cooks here, local or not. It's just part of being here.

Locals sometimes opt to buy onsen water to bring home for cooking, too. That costs around $1 for a liter. The water running through the town—the aquamarine, freezing-cold creek and the cloudy, scalding-hot hot spring—sustains life here. It has for almost two millennia.

Hot water ablutions are still performed during the spring festival at Kumano Hongu Taisha, providing a contrast to the cold-water rituals performed in local rivers and waterfalls. People still pray here. People still bathe here. And people still cook here. It feeds, it purifies, and it heals. Mostly, it's a good thing it feeds, because that sulfur-enriched food is surprisingly delicious.