January 26, 2012
In chapter 11 of Serpent of Time, Ryô spends the night at an onsen.
Unlike public baths (sento), where tap water is heated by a boiler, an onsen (温泉) or "hot springs" (the literal meaning) is fed by geothermally heated and therefore often heavily mineralized water.
Sitting squarely on the "Ring of Fire," Japan has no shortage of hydrothermal vents and no shortage of onsen. But seismic activity can also change the "character" of an onsen, or turn off the tap entirely.
Although the sento has declined in use over the past fifty years, the onsen has seen increasing popularity as what was once an upper-class luxury became a middle-class vacation destination.
Whether a corporate retreat or spring break, the "traditional" ryokan-style inn with an onsen has become practically de rigueur. The onsen is a travel show favorite.
Even the staid NHK doesn't shy from onsen travelogues featuring naked kids and naked butts (male only, sumo having made the male butt an inconsequential sight; on camera, women sport white bath towels).
Incidentally, "mixed bathing" (kon'yoku) can still be found a small number of onsen, though the typical Japanese would find them as exotic in actual practice as the typical American.
The onsen featured in chapter eleven is based on the Katsuragi Mishima Onsen at the Hidaka crossroads in Katsuragi.