When I was in Japan last year I was too timid to venture to any hot springs or onsens, since as a westerner I felt unsure about the customs of going to one. What are some recommended hot springs, and what is the experience like?
Onsen are the hot springs you will find around the ski reports (and everywhere in Japan). They are one of my favourite Japanese experiences. You will usually need to take a towel (for drying off later), a smaller towel to take into the water with you and shampoo and soap. But first you need to be naked and clean. So put all your clothes in the locker or basket provided. Then sit down on the small stools in front of the mirrors and shower hose. The custom is to wash well with shampoo etc. You might finish off by filling the nearby basin or bucket and tipping it over your head.
You may now enter the water.......... And its usually very hot so check it out first. Sometimes there are pools with different heat levels. There may also be an outside area or garden where you can sit, cool down and enjoy the atmosphere.
In cities there are still Sento hidden amongst the houses. These are the traditional public bath houses and are similar to onsen but often fairly basic. You will need to get directions from your hotel or ryokan. I highly recommend the experience. We went every night in Tokyo.
So you need to shed your inhibitions and enjoy that end of day soak in the seering mineral baths. Its soooo good. about 10 years ago
Going to an onsen is certainly a unique experience. As Tas_GC commented, bring both a small and large towel with you. Large towels are usually discouraged or completely banned within the bathing area, sometimes small towels are acceptable but I think it varies from place to place.
Once you go into the bathing area you need to wash yourself thoroughly at one of the little washing stations before heading into the pools.
It's worth noticing that some places also ban people with tattoos, essentially to stop Yakuza going there. I'm sure that if you had a little tattoo it would be fine, but people with large tattoos may have issues.
When looking to go to an onsen, find one that actually uses hot spring water, rather than the sento places that typically just use heated tap water. about 10 years ago
Hot springs are without a doubt one of the best things to do in Japan - i won't repeat about the towels as what they said above is right. However tattoos are completely banned. If it is small enough to be covered by a band aid it is possible to get in, but some places will even reject that. However if you can get a private onsen (more expensive but sooo much nicer!) then the rules are a bit more flexible.
But the key things to remember are - wash before and after the hot spring, never swim, just sit and relax and no drinking or eating unless stated otherwise (some private hot springs offer a food and drink course that can be had in the hot spring, but they are rare). And the small towel should never enter the water, it should only be used as a cover when you are getting in and out of the hot spring. almost 10 years ago