Onsen - Japanese Baths
An onsen is a Japanese Hot Spring, traditionally they are used as public bathing places
Onsen come in many types and shapes including outdoor and indoor baths. Baths may be either public run by a municipality or private company, often as part of a hotel, or Ryokan.
Onsens are a central feature of Japanese tourism often found out in the countryside, and are a major tourist attraction drawing Japanese couples, families or company groups who want to get away from the hectic life of the city to relax.

Onsen Features
Traditionally, onsen were located outdoors, although many are now found with indoor facilities. Onsen by definition use naturally hot water from geothermally-heated springs. Onsen should be differentiated from sento, indoor public bath houses where the baths are filled with heated tap water.
Onsen water is believed to have healing powers derived from its mineral content. A particular onsen may feature several different baths, each with water with a different mineral composition. The outdoor bath tubs are most often made from Japanese cypress, marble or granite, while indoor tubs may be made with tile, acrylic or stainless steel.
Traditionally, men and women bathed together at the onsen, as they did at the sentō, but single-sex bathing has steadily become the established custom since the opening of Japan to the West during the Meiji period. Mixed-sex bathing persists at some onsen in the rural areas of Japan, which usually also provide the option of separate "women-only" baths or different hours for the two sexes, although young children of either sex may be seen in both the men's and the women's baths.

Onsen and Sento Ettiquette
At an onsen, as at a sento, guests are expected to wash their bodies and rinse themselves thoroughly before entering the hot water. The indoor baths have faucets with removable shower heads and stools to sit on, for showering. A thorough body scrubbing and removal of all soap residue is very important before entering the main communal baths.
Whilst voyerism has been rare, in recent times there has been greater media interest in this problem. Often there is a bath attendant watching bathing areas, and once children reach a certain age they are expected to remain in the single sex areas.
In most onsen swimsuits are not allowed, but some will allow a small towel taken into the baths for modesty.

Tension in the Onsen
Some Onsen and Sento have now banned people with Tattoos due to issues between rival groups of Yakuza (and the nervousness of the general public on the entry of Yakuza members). Some bathhouses have also banned those of non-Japanese racial decent, more through fear of bathwaters being polluted by those unaware of customs than through any overt racial discrimination.