Campervan Hire Tokyo
Campervan Hire Tokyo - Wicked Campers in a larger map
Around the Kanto Region: Hakone/Fuji Lakes area (from Odawara), Boso Peninsula (from Chiba), Nikko and Oku-Nikko area (from Utsunomiya, Nikko, or Kinugawa Onsen), Ikaho or Kusatsu onsen area (from Takasaki).
Around the Kansai Region: Southern Wakayama Prefecture including Shirahama and Nachi Falls (from Wakayama or Nara), Ise Shrine and Ago Bay (from Nara or Nagoya), Amano Hashidate and Kinosaki Onsen (from Kyoto but avoid central areas), Akashi Kaikyo Bridge and Awaji Island (from Kobe).
Or explore Chiba peninsula (rent a car from Chiba city). Drive around the peninsula. There are two flower parks, a castle on a bluff, a mother farm, famous morning market town (Katsuura), aquarium, maybe head up to Choshi and see the lighthouse. Along the way is the longest sand beach in Japan. There are several road stops along the coastline.
During fall, depart from Takasaki and explore Gunma area. Overnight in Ikaho Onsen. Visit Lake Akagi (koyo and a walking path around the lake), Numata city (famous for the big red masks). There is a mother farm in the area, famous udon town. Kronenberg Ranch (German theme), and a bunch of other stuff. If you have time, Minakami Onsen and Tanigawadake cable car. Tanigawadake is reputed to be the tallest mountain in Japan which means it has some snow all year round.
For those visiting Osaka, a very convenient day trip right under your nose is Wakayama City. It is just 40' south of Kansai Airport. Easy two day campervan trip. Be sure to visit Kuroshio Market. There is a new European theme park next to Kuroshio market.
The Wakayama peninsula area, e.g., Kumano is very nice but distances are vast. From Nagoya a very enjoyable trip is to Toba (Mikimoto pearls) via Ise Jinja and Iga Ueno ninja place. Along the way is an 11-waterfall hiking trail next to a stream known to harbor those monster Japanese salamanders, a famous aquarium where kids can sit on a walrus, and am impressive Spanish theme park. You can take a boat tour from a harbor south of Toba. Stop off in Matsuzaka and have some of their famous wangyu beef. At fishmarkets along the eastern coastline you can buy live abalone and have it cooked or eaten sashimi style. This trip needs at least two days though as I was a bit rushed if you do the waterfall hike and especially if you spend much time in Ise.