Come Skiing in the World Powder Mecca of Niseko !
An Onsen is an open-air hot spring. In Niseko, Onsen's range from simple hotel mineral baths to luxurious pools but in essence the origin of the water must originate from a volcanic source.
At Niseko Grand Hotel, one of the few mixed-gender onsen, snowflakes melt just as they hit steam that rises in great wafts from the outdoor rock pool. At the Park Hotel there are seperate areas indoors. There are separate male and female changing rooms, but the onsen tradition is considered a great social leveller. All that protects bathers from baring all is a small white modesty towel used to cover yourself as you inter the spring.
The Niseko area has 16 onsens open to the public year round. On average adults will pay around ¥700 ($9.00 AUD approx) for a relaxing and therapeutic bath in naturally heated volcanic water.
Onsen to the Japanese are a way to relax and revitalise, many are rich in minerals which are associated with numerous health benefits, helping to relieve muscle and joint pain and arthiritis. 
But even if you don't have any serious ailments or injuries they are well known for the relaxing effect they have on your body.
Onsen hot springs are essentially a communal bath or sento and these days are generally single sex where women and men bathe seperately. Onsen ediquette is some what different from using hot springs or spas in other countires. One of the major differences is that bathers bathe naked using a small "modesty" bath towel while entering and leaving the onsen.
Diving and swimming is not allowed - the idea is to simply relax and allow the water to soothe and rejuvenate. Refreshments are available, a beer in an Onsen after a hard day on the mountain, you cannot beat it !