If you need to forget your troubles for a day, release your stress or simply pamper yourself, there is nothing like an Onsen! Onsens are hot spring bathing facilities that look nothing like any other bathing facilities anywhere else in the world: Yes, Korea and Taiwan has plenty hots springs, and it is not perhaps the first time you hear about other hot springs in the world. The baltic countries are known for their fantastic spas and who doesn’t dream about the a hot deep in Iceland’s volcanic waters. Yet there is something ceremonial and different about Japan’s onsens. If you are in Japan, it has to be listed as a must -do in your agenda!
So what is so special about them…Well, as a western foreigner there are things you might find amusing or very different. First of all, there are etiquette rules to be followed:
1. When you go to an onsen, leave your swimming suits home! This might be obvious for those who live already in Japan, but I still find it amusing everytime I see a friend who comes to visit for the first time how embarrassing is to bathe naked. It was also for me very difficult to an the beginning, but believe me you get used to it :p Traditionally, men and women bathed together (way back before the Meiji period, before Japan opened to the West), but single-sex bathing has now become the established custom . You can still find mixed onsens in some parts of Japan, but they are rare. If you ever see one, girls you can always were a towel wrapped around you. 
2. Towels!! You are not permitted in theory to take a towel into the bath with you. You may see some people with small towels on their heads (see the picture), but the etiquette indicates that dipping the towel is a no- no. You can also use the small towel for modesty while walking around.
3. Clean and Rinse yourself before entering the hot spring!!!! That is the most important rule!!! Hot springs are really for relaxing and to enjoy the minerals in it , however, you have to be completely clean before entering it. Most onsens will provide soap , shampoo and conditioner. If not, you can buy it from them. Use the stool to sit and wash yourself throughly (see below)
Where to go?
If you are in Tokyo, your best shot is to go to one of the Onsen’s meccas in this area: Hakone. You can take the Odakyu line from Shinjuku and buy a Romance car train ticket and it will take you faster than any other train. You can also take an express, but it does takes long from Shinjuku. A weekend could be the best option to fully enjoy your stay there. There are other onsens around Tokyo, ask your friends. If you don’t have time, you live downtown and still want to get a hot dip, try the “sentōs”, which are indoor public bath houses where the baths are filled with heated tap water. You will probably won’t get all the minerals from an onsen, but you will relax. My suggestion: If you live on the Odakyu and you don’t want to go all the way to Hakone, there is a fantastic black water onsen near the train station in Shin-yuriogaoka (shuttle bus available) :
or one near Machida, but not easy to access by foot:
Enjoy!!