Onogawa Onsen (小野川温泉) is a hot spring village in Yamagata, Japan. It belongs to the city of Yonezawa but is covered separately here.
Glowing in good health
Onogawa is one of Japan's most radioactive hot springs, with radon concentrations of around 10 nanocuries per litre (200 Bq/m³). That's not quite as scary as it sounds though: worldwide average household background radiation is around 2.5 nCi/L, so a half-hour dip is no worse than two hours spent watching the TV. However, the water is also quite sulphurous, so expect bad egg smells.
Onogawa crops up regularly on lists of snowy hot springs, with a high probability of heaps of the stuff as early as December. It's reasonably accessible from Tokyo, boasts one of the better-preserved "olde Japan" villages in the north, and makes a decent base for low-key skiing in winter as well as firefly-spotting and hiking in summer.
The nearest train station is Yonezawa, two hours from Tokyo by Yamagata Shinkansen, while the nearest airport is in Sendai. Yamakō Bus runs from Yonezawa station to Onogawa, but the service is very infrequent: six buses per day, running roughly every two hours 8:05AM-6:35PM. The trip takes 20 min and costs ¥600. If you miss the bus, it's around ¥3000 by taxi.
Onogawa can be covered quite effortlessly on foot.
Not much, to be honest. In summer, fireflies (蛍 hotaru) can be seen at night near the river. There's also a little shrine devoted to the hot spring (湯の神社) and an even smaller temple of the "Tofu Jizo" (豆腐地蔵), but both are often snowed in and inaccessible in winter.
The main thing to do in Onogawa is hot spring hopping. All inns sells a "Yumeguri Plan" (夢ぐりプラン) ticket that lets you sample any three baths in town for ¥1000, either at hot spring inns or the two public hot springs, Amayu (尼湯) and Takiyu (滝湯). If it's outdoor hot springs you're after, Kajikaso (河鹿荘) and Kameya Mannenkaku (亀屋万年閣) will be your best bets, but check schedules beforehand as hours are limited (noon to 4PM only at most inns).
In addition to full-body baths, there's a scattering of ashiyu (足湯) foot baths, which are handy for defrosting your feet after stomping about in the snow.
If you're here in winter, there's one more amusement option:
There are a couple of souvenir, alcohol and convenience stores along the main road. Local products of note include tamakon kon'nyaku (devil's tongue) jelly balls and mamemoyashi bean sprouts.
Most visitors will have breakfast and dinner at their inns, but there are a couple of simple eateries and izakayas in town.
There is a small tourist office in the center of town, although opening hours are sporadic.