Arima Onsen is one of Japan's Three Old Hot Springs, with a recorded history going back to the Nihon Shoki , published in 631. The waters of Arima come in two flavors: the Gold Spring (金泉 Kinsen ) is yellow-brown thanks to iron and salt, while the Silver Spring (銀泉 Ginsen ) is colorless but mildly radioactive.Technically, Arima Onsen is a part of Kobe, but it's on the other side of Mount Rokko and thus a separate city for all practical purposes.