Nagano Side Trip: Jigokudani Monkey Park
Jigokudani literally translates as Hell Valley, and is a common name used for valleys with hot springs - usually ones with active volcanos, sulfurous streams and steam vents. The most famous one is in Hokkaido, but Nagano's is easier to get to and possibly better. While I say Nagano, this Jigokudani is in Nagano Prefecture, but actually in Yamanouchi city. The area's also known for hot spring resorts and ski resorts.
Getting off at the Kanyabashi Onsen stop, the first thing you see is a folklore museum. I arrived late enough in the afternoon that I didn't have time to visit it. From there, you should probably have a map; there is one Japanese map near this museum, which will help you get to the trailhead. Essentially, you follow one road, make a right at the dead-end, and follow that up the hill to the start of the trail.
Once you reach the park itself, you pay your admission and start to see monkeys. There are signs along the path warning you about having food, and I've heard first-hand accounts of monkeys going into bags, backpacks, and more because they can smell your stash. There are pay lockers at the entrance to the park if you absolutely must bring food to the park, and I don't recommend having any with you once you enter.
Coming from Nagano Station, visitors can catch a fairly direct bus. Ask at the visitor's center for information on which bus to take and to get an updated schedule. As I mentioned earlier, get off at the Kanbayashi Onsen stop and walk to the start of the trail, following the trail to the park. The hike itself takes about 30-40 minutes depending on how quickly you walk, if you stop for photos or a rest, etc. Bring water for the hike; there is nothing out there and I don't remember seeing vending machines anywhere.
The best time to visit is probably in the winter, when the snow is on the ground and the monkeys are highly likely to be in the water keeping warm. Apparently the monkeys are a bit erratic in the fall, but you get great fall colors in the hills and I saw plenty of monkeys at and in the hot spring. I saw the monkeys fighting a bit as they are always trying to move up the hierarchy, but nothing serious - a friend who visited about a year prior said that they were quite violent. Spring and summer will be the most comfortable for hikers, but the monkeys are less likely to get wet when they're already warm. The trail from the bus stop is passable year-round, but it will be snowy and cold if, well, it's snowy and cold outside.