What are some of the best recreational bike-riding routes in the part of Japan where you live?

Don't do a lot of cycling, but I quite enjoy riding along the Tama river. Wouldn't say it's one of the best by any means though.

I ride every day on single tracks. But in Japan the rivers have some great rides flat and scenic most are. I dislike hills and avoid them.

The cross-country skiing trails in Nikko, although not during winter for obvious reasons.

might be overstated, but the coastal highway near Enoshima. Any anime fan or just someone who appreciates a good seaside view will love it, guaranteed. That and basically any mountain pass, the route to Takabocchi highlands in Nagano is also nice.

Shimanami Kaido is great.

Ome Kaido starting in Okutama.

From Nikko to Oyama next to the Ta River (Tagawa).

Route 292 up Shiga Kogen and over the border to Gunma. Its the highest "kokudo" road in Japan and puts you above tree line up in the mountains. Its a massive climb, but well worth it. There is also a great climb up Mt. Norikura near Matsumoto, a road closed to traffic, that goes up to 2700m but is more gradual than the Shiga Kogen climb. On the other side of Matsumoto, Utsukushigahara is a great climb too, with a wacky Bubble-era open air art gallery at the top. Above tree line is special, open scenery and feels like you are in the Tour de France.

Cycling is being targeted by Japanese tourism associations, so beware of payola hype (like Shimanami Kaido) and routes with lots of tunnels being promoted by clueless tourism bureaucrats who do not ride bikes but have been told to get people to go to xxx mura to eat their very special noodles. A lot of best cycling in Nagano is from (quaint nowhere village with lots of old houses) to (quaint nowhere village with lots of old houses) via zero "famous" sites but using back roads with zero traffic.

When I lived in Nagano, my only transport was a mountain bike. I cycled most days when there was no snow. Averaged more than 50 km. My favorite was cycling to Hakuba.

I enjoyed cycling up the Shimanto river during the rainy season on my fixed gear minivelo.

No people, little traffic,and beautiful scenery evocative of old paintings if misty bamboo forested mountains with old houses here and there.

Did the Shimanami kaido 10 years ago on Bromptons with my daughter on the rear rack,then across to Oita and down to Miyazaki and Kagoshima.

To be honest, there's so many forest roads and super-rindos,you are spoiled for choice.

Winter down here in the Ryukyus, before January is the best time for bikepacking.

Riding alongside the Kano River from Numazu to Shuzenji is very scenic and relaxing, as well as beginner friendly. After Shuzenji Bridge, it divides into the Kano River, the Ōmi River and the Katsura River. So far this summer, I've followed the Kano to the Jōren Waterfall and the Ōmi to the Ikadaba wasabi terraces. All kinds of uphill riding around Izu but the beautiful scenery and rustic charm make it worth the effort. I believe following the Katsura will take you to the Nishi Izu Skyline, which I'd like to try at some point (looks a bit higher than Hakone).

I rode the Nikko Kaido between Utsunomiya City and Nikko on my mountain bike. The stretch through the cedar trees in nice but the rest isn't particularly exciting. It just goes through typical dying Japanese towns. After Nikko though, are the 48 hairpin turns of the Irohazaka which is a lot of fun. Up to Chuzenji Lake and Nantai-san. Coming down the Irohazaka was the highlight, of course. Went back through the abandoned copper mines of Ashio.

Between Yokohama and Tokyo I really like riding along the route of the Old Tokaido.

Might take a while, but you can go right around Lake Biwa.