This last weekend I researched and tried a new cycling route, which turned out to be about 59 km. The route goes through Totsuka, Shonandai, Up the Mekujiri River on a bike path ("jitenshado" 自転車度), across Zama to the Sagami River, Down the Sagami on some trails, and back across to the Mekujiri River bike path via Ebina. I entered the route on Google Maps so other English-speaking cyclists in Japan can enjoy it.
Riders should note, that the Mekujiri RIver Bike Path has sections where every 100 meters there is a "gate" you have to swerve through ostentatiously to keep speeds down. If you want to just ride straight and fast, the Yamato Fujisawa Jitenshado is better. Also, the Sagami River bike path is not so much bike path but rather more trail, and is still underdeveloped and so would not be appropriate for a road bike. I read online that they are building a proper bike path along the Sagami River, which is due to be complete in 2011. I tried to pick routes where if the route was along a road, at least there was a decent sidewalk available to use, for riders who are still a little nervous about riding on the road directly.