An onsen is a natural hot springs in Japan. While “onsen” refers to the hot springs themselves, many people use the term to refer to the inns and bathing facilities which surround the hot springs, and visits to regional onsen are very popular with the residents of Japan. Visitors to Japan may also make time to visit an onsen or two during their stay, as hot springs and communal bathing are a large part of traditional Japanese culture.

Japan's volcanic nature has created a plethora of geothermal springs which are scattered across the country. Some onsen are relatively private and known only to locals, while others are major vacation destinations. Bathing facilities around onsen typically feature lodging as well, which may vary from traditional Japanese inns known as ryokan to more conventional hotels. In some regions, an onsen is run as a municipal enterprise, while in other instances, the springs are privately managed.

Visitors to an onsen typically have a number of hot pools to choose from, including both indoor and outdoor pools. The temperature and mineral composition of each pool varies, with some onsen classifying their pools by the minerals present in each. Many people believe that certain minerals such as sulfur are beneficial, viewing onsen as a place for healing as well as relaxation.

Japanese people have been visiting onsen for centuries. Around the 1800s, European visitors to Japan often remarked on the onsen, and they became a popular spot with tourists. Somewhat unusually in Japan, the atmosphere at an onsen is very casual, and people are not divided by social rank. Many of the strict rules of personal conduct are relaxed at onsen, and the overall feeling is one of parity and equality, not least because people enjoy the pools nude, whether they be heads of major corporations or lowly street vendors.

In addition to the hot pools, some onsen establishments also offer food and massage. Ryokan typically provide traditional Japanese meals to their guests, and visitors who just want to use the pools without spending the night may be able to order meals as well. People who wish to visit an onsen should definitely consider going to a ryokan for a traditional Japanese experience, and making reservations is well-advised.

There are a few rules of etiquette at the onsen with which gaijin (foreigners) may want to familiarize themselves. Many onsen have gender-segregated pools today, so visitors should make sure that they are entering the right area. Robes, towels, and personal possessions are traditionally left in cubbies, with bathers taking a small hand towel to cover their privates for modesty. Before stepping into a hot pool, bathers step into shower cubicles to wash themselves carefully, taking the time to rinse away all traces of soap. Bathers should step into the pool carefully, ensuring that they do not splash or disturb other patrons.