Since this route takes you through one of the nicest areas in the Japan Alps, there are so many great places nearby that listing all of your "Alternatives" could take quite awhile. Here are a few of the more obvious ones:

Norikura just happens to be right next to Kamikochi, one of the major departure points for hikers (and you can see the famous view from the top as you go down Norikura). The ride up to Kamikochi is quite an experience, particularly the last tunnel - very steep, a terrible road, and absolutely pitch-black. A friend dubbed it the "Wormhole from Hell"... so consider yourself warned. You could visit Kamikochi first, then take route 158 to the road leading to Norikura. You could also (1) take the rindo (apparently it’s fully paved now) down from Norikura to route 158 and then cycle a couple of kilometers east to the road leading to Kamikochi, or (2) cycle all the way back to route 158 (downhill, it would be fairly quick) and then struggle up through the tunnels and traffic until the turnoff (about 12 kilometers). Either way, the scenery at the end is worth it; just give yourself at least a day or two there to do some hiking and truly enjoy it.

Takayama is worth a trip all by itself, and here is one more reason why: at the Hida Folk Village, they've collected dozens of thatch-roof houses from the Shirakawa area that would otherwise have been lost due to dam construction, and the reconstructed village has been very tastefully put together. Volunteer guides demonstrate crafts and talk about the history of the area. It's an easy bike ride from the city center; follow the signs or ask for a map at the information booth in front of the main train station.

If the houses of Hida aren't enough for you, you can always go to the source: Shirakawa was recently declared a UNESCO World Heritage Site, and it's easy to see why: a preserved village with more than a hundred old houses of the steeple-roof construction known as gassho-zukuri (hands-in-prayer). Be sure to spend the night in one (many are minshuku) for the full experience. Head northwest from Takayama on the road across from the river from route 41, then keep on in the same direction on route 471-472, and finally turn left on route 360. Note that this is a 1289m pass and is closed in winter and early spring; check to make sure the road is open.
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