Hakone Onsen

From a post town on the Tōkaidō

Hakone's oldest spring, at Yumoto, is traditionally dated to 738 (Tenpyō 10), attributed to a wandering Buddhist priest. The waters entered the national record only much later, when Toyotomi Hideyoshi's army rested in Sokokura during the 1590 Odawara campaign, and when the Tokugawa shogunate fixed the Tōkaidō highway through the mountains. By the Edo period seven onsen villages had coalesced into a known set, the 箱根七湯 (Hakone Nana-yu): Yumoto, Tōnosawa, Dōgashima, Miyanoshita, Sokokura, Kiga, and Ashinoyu. An 1811 guidebook catalogued each by smell, taste, temperature, and reputed cure. Tribute water was sent up the road to the shogun in Edo. After the Meiji opening, deeper drilling added Gōra (admitted in 1919 with the new Hakone Tozan Railway), Kowakudani, Sengokuhara, Yunohanasawa, Ashinoko, and several more; together they form the modern roster of 箱根十七湯 (Hakone Jūshichi-yu).

Seventeen springs, six distinct quarters

The seventeen are not one resort but a chain of villages strung along the caldera. Yumoto, where the Hayakawa and Sukumo rivers meet, is still the busiest gateway: most ryokan, most onsen sources, the steepest concentration of day-bath options and souvenir shops on the way up from the station. Tōnosawa sits a single switchback above, known since the Edo era as a quieter literary quarter. Miyanoshita climbs higher, dominated by the Fujiya Hotel, opened in 1878 as one of the first Western-style hotels in Japan and a host over the decades to Charlie Chaplin, Helen Keller, Albert Einstein, and the Shōwa Emperor. Gōra and Sengokuhara sit on the upper slopes, with broader skies and the open-air baths that catch Fuji on clear winter mornings. Ashinoyu and Ashinoko, ringing the lake at around 700–950 m, are the highest and the coldest in winter. Spring chemistry shifts noticeably across the chain, from the mild alkaline simple springs of Yumoto to the sulfur and acidic waters near Ōwakudani.

A landscape full of museums

Hakone is unusual among Japanese onsen towns for the density of its art institutions. The Hakone Open-Air Museum in Ninotaira (open since 1969) threads Henry Moore and Niki de Saint Phalle sculpture through the hillside; the Pola Museum of Art in Sengokuhara holds an Impressionist collection in a low building cut into the woods. Both pair naturally with a soak: a half-day of galleries, an evening in the bath.