Question: Where is eating a black egg healthy, bathing in brown water encouraged, and soaking in acid great for your skin?
Answer: Japan’s onsen (hot springs)
Beneath the surface of Japan lies a literal hotbed of volcanic activity—which bubbles to the surface in the form of hot springs. For centuries, the Japanese people have embraced these curative waters as an important part of their culture, both for their medicinal properties and as a way to relax and destress.
The term onsen refers to both the hot spring itself and the bathhouse built around it. And while the word may be generic, the experience is anything but. There are some 3,000 onsen in Japan, varying greatly in size, luxury, landscape, temperature, and medicinal benefits. Even the color—and odor—of the water changes depending on the minerals contained within.
As with many aspects of Japanese culture, it can be complicated—so here are some tips on navigating the waters of Japan’s famous hot springs:
- Perfect prescription: There are 11 official categories of onsen based on mineral content. So-called simple onsen contain the lowest concentration of minerals, making them ideal for those with sensitive skin. At the other end of the spectrum, radioactive onsen contain trace amounts of radioactive material—which, in such miniscule quantities, actually benefit the body. In between, bubbly carbon dioxide onsen can reduce blood pressure; alkaline sodium bicarbonate onsen cleans and smooths the skin; iron-rich ferruginous onsen helps with anemia; and (putting it mildly) strong-smelling sulfur onsen heals blemishes.
- Up your dosage: Depending on the makeup of the water you’re bathing in, you may gain even more health benefits from drinking it. If so, you’ll see taps and cups to indicate this, or the onsen will sell it in bottles. Another popular way to ingest onsen minerals is to cook an egg directly in the bath water. Because the temperature is hot but not boiling, the egg comes out soft-cooked: silky whites with a barely set yolk.
- A side of sulfur: While soft-cooked onsen eggs are a delicacy, the black eggs of Owakudani—literally, “the Great Boiling Valley—are decided more indelicate. Here, the water is hot enough to actually hard-boil the eggs. But what truly sets them apart is the soot-black color, caused when the sulfur in the water reacts with the eggshell. The sulfur leaches into the egg itself, too, making it something of an acquired taste—but worth it for those who believe the local legend that eating them adds years to your life.
- Follow the rules: As with many aspects of Japanese culture, the onsen experience comes with a strict code of etiquette. We’ll stick with the basics: Remove all clothing and store it as directed; you can use your hand towel for modesty. No clothing is permitted in the bath. Wash thoroughly before bathing, using the soap provided. Bathe in increments of 5-10 minutes, resting on the rim of the bath in between; do not exceed a total of 30 minutes. After your bath, use your hand towel to wipe off as much excess water as possible before returning to the changing room. While you can shower if you like, rinsing will weaken the effect of the minerals.
- Guilty by association: There is one thing you’ll need to cover up in an onsen. If you have a tattoo, be prepared to hide it with a bandage or a specially-designed sticker—sold in Japan for this very purpose. While some onsen are relaxing this rule as tattoos become more mainstream, traditional Japanese culture associates them with the yakuza mafia.
You’ll have the opportunity to experience a Japanese onsen when you join O.A.T. for Japan’s Cultural Treasures.