Japan by bike (train, bus, ship and plane): Best cycling experiences

Bicycle touring Japan - Top 10 cycling experiences

Here my personal top 10 bicycle experiences in Japan:

Multiple cycle roads available. They are of varying quality from high speed cycling road along the river between Kyoto and Nara to partly overgrown lanes or gravel. But overall it is a very long cycling trip in which one can use on-and-off cycle lanes.
Good cycling lanes around Lake Biwa, with nice views on the lake and not the typical "river ride".
Specially around Nara there are also a lot of sign posts specifically for cyclists.
Great area with a lot of touristic highlights, even outside the obvious destinations

Small roads with little traffic leading through wonderful country side and well preserved and still functioning villages, including some sightseeing options (temples, shrines...) which are void of tourists.
In the center between Ryotsu and Mano Sado island is quite flat, but for the more ambitious cyclists there are two ranges of mountains on each side of the island to explore.

I originally had decided to go to Tono valley because I heard of a good cycling infrastructure there. Well there is the typical cycle path along a river, however the valley has a lot more to offer, with having small streets with little traffic.
The local tourism office has some maps for suggested rides
Very nice landscape with still a lot of traditional houses
I did not ride INTO Tono valley by bicycles but rather by train (because of hills and of rain), however the part I did cycle up from Shin Hanamaki to Iwanebashi was also nice. No bicycle lane, but not a lot of traffic anyway.

Wide cycle lane through the forest between Sapporo and Kitahiroshima.
In some points totally quiet, which I appreciated even more after riding in the traffic of Sapporo city.
Gently sloping up and down, as it is an old train track
It is relatively short though.

Long totally straight cycling lane out from Tokyo to Sayama Lake used by both neighbourhood cyclists as well as people going more seriously to Sayama Lake
Links to a quite long cycling path out of Tokyo, you can essentially start in Shinjuku (or maybe even before), ride down along Kanda river to Kichijoji, then through small neighbourhood streets until somewhere behind Koganei park, get on the cycling road there (see map in the link below) and then ride slowly up to the lake and make a full round of the lake on the cycling path before returning back to Tokyo.
Easy accessible from downtown Tokyo

A long stretch along the Pacific ocean with views of the ocean and farther into Irago peninsula through fields
The one big problem however is the maintenance of this cycle path. Besides a few perfect stretches (like the one leading from somewhere outside of Shizuoka to Omaezaki on an old railway track or the last few kilometers leading to cape Irago) it has a lot of totally overgrown parts that can become totally impassible and specially between Omaezaki and Hamamatsu the sand dunes on the path are a real problem.
Apparently nothing is being done against the vegetation. A bit more is being done against the sand, but for the time being I only saw statements of that something WILL be done, no results yet (unless the path was even worse before)