About

What this is

There is no shortage of onsen listings. What there is a shortage of, in English especially, is anything that models Japanese hot springs the way Japan actually does — as water first, and buildings second.

So this site is built on three things that other guides flatten into one. A 源泉 is a spring source: a specific hole in the ground with a temperature, a pH, and a chemical analysis. A 施設 is a facility: an inn or a bathhouse, which may draw on several sources, or share one with its neighbours. A 温泉地 is an onsen area: a village or valley that grew up around the water. Filters that treat these as the same thing produce the results you have already been disappointed by.

What we promise

Every fact that can be cited is cited, and you can see which ones are not. A source marker beside a price means someone read that price off a sign or a website and recorded where; no marker means nobody has, and you should treat it accordingly. A page that cited nothing would prove nothing, which is why the contrast is visible rather than hidden.

Every entity shows when a human last verified it. Onsen close, prices rise, and the 混浴 bath your guidebook promised became women-only in 2019. A date you can see is worth more than a confident page that is quietly four years stale.

Closed facilities keep their pages. Nothing here 404s because a place shut down — you get the page, with a banner saying so. Finding out is the point.

What this is not

It is not a booking site, and it takes no commission from anyone. Nothing is ranked, promoted, or sponsored.

It is not medical advice. 適応症 and 禁忌症 are reproduced because Japanese law requires facilities to post them and because omitting the contraindications would be unsafe — not because they are clinical guidance.

It is not finished. The corpus is deliberately small and deep rather than large and thin; a thousand entries with nothing in them would be easy and worth nothing.