Hot springs, known as onsen in Japanese, are a popular attraction in Japan. They are natural hot water baths that are believed to have healing properties due to their mineral content. In Japan, hot springs are often found in mountainous areas, and there are many hot spring resorts throughout the country.. Visit the fabulous Osaka Bay Tower to access the fun-packed Solaniwa hot spring Onsen. Try multiple facilities such as carbonated bath and silk bath for ultimate relaxation.