There are two paved roads into the valley. The main route from Ohata (15 km away) and Mutsu has one (1) bus per day at 8:40 in the morning, while the shortcut connecting to Mount Osore has none. A dirt trail, navigable by 4x4 in summer, traverses through the valley to the remote west coast.
Oku-Yagen has no less than three excellent open-air hot springs, all offering views of the Ohata River rushing through the valley:
Meoto Kappa-no-yu (夫婦かっぱの湯), near the end of the paved road, is a modern state-funded operation offering sex-segregated open-air baths with dressing rooms and showers. Open 8:30 AM to 18 PM daily except Tuesday. Entrance fee is only 200 Yen for adults.
Kappa-no-yu (かっぱの湯) is the original hot spring, past the bridge at a fork of the river. The baths consists of two bare-bones dressing cabins and a large rock pool of hot water. No services, but no entry charges either and always open.
The unnamed third hot spring is on the river side of the road before the other two, unmarked except for a "ゆ" scrawled on a roadside post. A path leads down to two concrete tubs, one filled with warm water, the other filled with (very) hot water. There are no dressing rooms or other concessions to modesty here, but the views of the Otaki rapids are unparalleled and more often than not you'll have it all to yourself.
Pretty much the only other form of entertainment is hiking. A very picturesque forest trail runs along the side of the river between the two hamlets, partly on the tracks of an old mining railroad. The fall colors in the valley are particularly famous.
Yagen Campground (薬研野営所, Yagen-yaeijo), at the entrance to the valley within walking distance of the springs, offers lawn space for 500 yen per person, toilets and little else. An excellent budget option if you're self-contained.
Mount Osore, the gateway to hell of Japanese myth, is a half-hour ride away on a squiggly mountain road.
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