Dogo Onsen in Matsuyama is said to be the oldest hot spring in Japan, with a 3,000-year history. Over the years, emperors and ordinary people alike have recuperated in its soothing alkaline water. The main bathhouse is a complex of connected wooden buildings that were built by master craftsmen between 1894 and 1935. The result is a slightly eclectic mix of architectural styles and labyrinthine passages, with luxurious stone baths as well as tatami rooms for post-bath relaxing. The Yushinden is a series of lavishly decorated private rooms and a bath built exclusively for the imperial family. You can tour the rooms for a fee.