I rode this ride with my friend Toru yesterday, doing it "no rinko" style myself (204 km in about 15 hours).
We started from Setagaya at 05:30. Based on @Directeur's RWGPS data and times from my previous rides out to Takaosanguchi, I reckoned we would be able to make it to Odakyu Shin-Matsuda station by 14:00, for my friend to head back to Tokyo for prior commitments in the evening, while I would cycle back home.
Everything went pretty much according to plan. We left on time, made it to Takaosanguchi about 30 minutes early and also arrived at Shin-Matsuda station half an hour early. We followed Rt76 pretty much all the way from Sagamiko to Shin-Matsuda. Here is the dam just before Doshi road:
In Aone village we found two shops right across the street from each other, one of them selling fruit, milk and other fresh food.
We topped up our water and had some bananas. Then we headed up past the campsites, past the road signs that warned of the closed road ahead. It's easy to miss the turnoff from the Doshi road (Rt413) onto Rt76 just before the prefectural border because it's only signposted for the camp sites, it doesn't mention Rt76 at all.
The closed part of the route on the Doshi side was pretty bad, with places like this:
The word "post-apocalyptic" springs to mind: You start to feel like you're in some country or on some planet abandoned by its former human population, with nature gradually reclaiming it all. Numerous rock slides have been awaiting cleanup for ages. The tunnel at the top is still in almost mint condition, and so is a fairly new looking steel bridge on the Doshi side.
These are somewhat typical pictures of the road surface that awaits you:
Rather than just pedaling, you always have to plot a course that avoids the roughest spots ahead and every now and then you have to make a decision to stop and dismount and then push your bike for a while.
Some places were extremely muddy, in other places small streams ran across the road, leaving you ankle deep in water if you were to walk.
On the other hand, it never really felt dangerous. We were concerned about tire damage, but I had brought two spare tubes, one spare tire (which I don't normally carry even on long brevets) and a can of sealant. I don't think I would fancy cycling this on my own though.
For me the biggest "Wow!" moments where the numerous waterfalls we passed.
This one had a convenient viewing platform in front of it, but the access path to that was totally buried under the debris from a huge rock slide:
The views from the top were nice too.
Once we got through the tunnel, the descent on the other side was fairly easy and the road in mostly good condition. There are more campsites and then the lake. The scenery along the river is nice, big white boulders, turquoise water and many trees, but I didn't take any more pictures as we were rushing for Shin-Machida.
While I was climbing the washed out wild gravel tracks (even on my 42 mm 650B tires), I said to myself: "This is stupid!" But at the same time I know I will go back there, taking more time for pictures of the waterfalls and the other views that await you on "The Wild One."