Tennen Onsen Naniwa-no-Yu, also known as Natural Hot Spring Naniwa, is a spa nestled in the heart of Osaka. At a depth of 659 metres, the naturally carbonated mineral waters are brought to the surface via pumping. The hot spring water is also called "the beauty bath," as the minerals are said to be good for the skin. This public bath-style hot spring is located on the top floor, with an outdoor bath offering a serene escape with views of Osaka city.