From movies like Spirited Away to live action comedies like Thermae Romae, Japan is really known for it’s hot spring baths (onsen)♨️. We both love hot springs, and especially the towns that grow up around them. They are steeped in history and without fail have provided us with good food and relaxing times.
There are onsen all over Japan, even big cities like Tokyo and Osaka will have bath houses. These big city bath houses are often huge. For example Osaka’s Spa World is a huge multi level onsen with pools that can hold hundreds of people. It’s like a naked water park almost. Oh did I mention that all onsen are naked? Well nearly all, they are sex segregated and have a long list of rules and customs. A very few (less than 5%) of Onsen’s will have a mixed sex area with bathing suits. Many onsen towns will have foot baths and occasionally a public free outdoor onsen that is mixed sex with bathing suits, but well over 95% of onsen that you visit will be separate baths for men and women.
This infographic from itsyourjapan.com sums up the rules nicely. Mostly they are the same rules as you would expect at a public pool, except naked. The rule that catches some newcomers by surprise is the prohibition of tattoos. With the 2020 Olympics in Tokyo this rule is being relaxed by some onsen hoping to get more foreign tourist money, but as of 2019 we have only see one onsen that would allow tattoos.
If you want to visit an Onsen in Japan you should ask yourself what you want to experience. If your goal is just to get clean and relax in some hot water, pretty much every onsen will get you there! But there is so much more to Japanese onsen. Some are known for healing properties, and in fact every onsen will have a plaque somewhere that describes the natural minerals in the water. This is what people talk about when they say eastern medicine!
In general I can break down the onsen into three categories. Big city onsen, which are clean and sterile. Historical Onsen Town Onsen , which often feature a lot of natural wood and stone, and specialized onsen, which may contain more acidic water than normal or other special benefits like snow monkeys that hang out.
Onsen Town Onsen!
These are probably the most well known and the most romantic that will remind you of spirited away. A town may have a dozen or more onsens within a square km walking distance. Some will be outdoors, some indoors. Many towns have a pass that gets you into all of them, or a certain number of your choice.
Hotel with Onsen not in an Onsen town
Many hotels in Japan, even in big cities, will offer an onsen. These often vary with the quality of the hotel. They more fall into the “hot water pool” than onsen proper, but sometime the water is still sourced from somewhere with decent minerals.
Big City Onsen
These onsen are mainly nice if you want to get clean, and have a soak in some hot water. There is nothing wrong with this, and often they will either add minerals or have a natural source. In Okinawa there are a few which use sea water piped from deep underground for warm temperatures.