For those wanting to do something a little different, consider this unique (if not a little bumpy and chilly) exploration into the heart of the Kurobe Valley, running from Unazuki to Keyaki-daira, in tiny train carriages (originally used for the construction of the Kurobe Dam system). When you're not careening through seemingly endless tunnels, the views of the surrounding mountains are breathtaking, especially in autumn, and the opportunity to explore some truly remote and astounding mountain rotemburo (outdoor baths) and inns is definitely rewarding.
The new Kurobe Unazuki Onsen Station on the Hokuriku Shinkansen line has dramatically improved access and increased visitor numbers. From Shin-Kurobe Station (adjacent to the shinkansen station), catch a local train to Unazuki Onsen Station (¥630, 25 minutes), from where it's a short walk to Unazuki Station, terminus of the Kurobe Gorge Railway.
You must purchase tickets for each leg of the journey separately at each station; due to high passenger demand, this is not a hop-on, hop-off service. The entire journey from Unazuki to Keyaki-daira takes about 80 minutes. It's suggested you take the full journey, and, along the way, decide which stops you'd like to get off at on the way back. For full details on how to get there, what to see and how it works, refer to the website.
The remote Kuronagi-onsen is a must-see: look out for bears along the path. Also recommended is the Iwa-buro cave bath, a short walk from Kanetsuri Station. The restaurant at Keyaki-daira can get very busy at times – bring sandwiches and snacks with you for the journey, as well as some warm clothing: even in summer it can get very chilly in the tunnels.
Be sure to sit on the right side of the train for the outbound journey from Unazuki, and the left side of the train coming back, or you'll miss the best photo-ops and develop resentment towards your neighbouring passengers: carriages are allocated, but seats aren't reserved and it's first-come first-served.