An Onsen (温泉) is traditionally a hot spring heated by the geothermic energy of Japan's many volcanos. Being a volcanic island, these hot springs are very numerous, with various chemical elements making them each unique. To be classified as a natural onsen the temperature must be at least 25° Celsius before being reheated to approx 40-42° Celsius (that's 107.6° Fahrenheit!). Many onsen are certified as natural and make claim to what elements are in the water. Japanese people believe the various elements lend healing powers for helping with aches, pains and muscle soreness among other illness cures. While this can't quite be proven, it is definately a good source of relaxation after a long stressful day in the city.

Onsen are quite numerous in rural areas and even in big metropolitan cities. However, you are likely to encounter 'fake' onsen or sentou （銭湯）which is a indoor bath with heated tap water. Don't confuse indoor onsens with sentou, however, as many natural onsens are indoors.

On a map you can usually find the symbol for an onsen as ゆ identifiable for Children or with the chinese character meaning the same thing: 湯. Sometimes there will be an icon on maps that looks like a little circle wavey steam lines coming out of it.

Onsen vary in cost and rules but generally you can expect to spend somewhere between $5 and $30 depending on the location and size. The rules at an onsen are pretty straightforward an easy to follow. If you have a contagious disease, stay away. And if you have large, prodominent tattoes, don't even think about entering (it's a long standing tradition to bar people with large tattoes on the basis that they represent the Yakuza elements of Japan).

Once you've entered an onsen facility you will be seperated based on sex and provided with a location to change and store your clothes. Sometimes this will be just a basic basket and other times you will be given a locker and key to take with you on a wrist band into the bathing area.

At this time, you are expected to get completely naked. The only thing you should bring with you to the onsen is a hand towel to wash yourself with and if necessary some soap and shampoo should the onsen not provide it already.

That's right, naked. This is not a typo.

Once you've undressed you can proceed to the bathing area, usually seperated from the changing area. Here you are expected to bathe yourself before entering the warm water pools. You should wash yourself thoroughly at a station which usually provides a stool, bucket, soap and shampoo and a mirror to shave in if you are a male.

The actual onsen usage procedures are pretty straight forward. There are generally a number of different bathing areas with different types of water and elements present within. Sometimes an outdoor area is provided and you can step outside into the cool weather if winter or the humid air in summer.

The usual procedure I follow is to soak for a few minutes inside, walk outside and soak some more. Rest and maybe go to the sauna if there is one provided. Sometimes there are sweat houses which have herbs boiling in the middle of the room.

My favorite part of most the onsen is the cold water pool. Usually there is a pool of frigid water between 14° and 20° Celsius where you can literally turn yourself blue then jump into the hot water section. It's quite challenge, so I suggest only those with enough courage attempt it. =)

After an onsen it is common to take a nap in the rest area while wearing a Yukata. Eat some Japanese Soba and drink some alcohol. Usually you go to an onsen as a family or couple with your coworkers and friends and are just there to generally relax. There is definately not much to it and it's a simple pleasure to rest and relax in the onsen. I've read that it's part of the cultural bonding to strip naked with your colleagues and friends to create cohesion in the group; whether this is true or not I cannot attest too as I have not done so with any of my colleauges, but it is great to go with a friend so you can chat as it can be quite boring alone.

It's generally not allowed to wear a swimsuit in an Onsen, sometimes towels are permissable unless your at a family resort and it's a mixed atmosphere (for the swimswuits).

Being noisey is not a good idea you can be asked to leave as it's a relaxation spa not a playground.

Mixed onsen are around in rural areas but generally it's all seperated.

Towels are not supposed to be dunked in the water at some Onsen as it's considered unclean, it's better to make sure not to do this just in case.

Children of both sexes will be in the onsen on either side so do not be surprised if 5 year old girls are watching you bathe.

Pubic hair in Japan is not trimmed, so expect to see a lot of hairy people, try not to stare (of course, if your shaved they will stare at you).

White people aren't often in the onsen so when they do go be prepared for people to stare (as if they don't stare enough as it is). Just ignore them and usually they will ignore you too!

Finally, did you know that Monkeys love the onsen too?!