One park to the next
A great cycling course for all skill levels is the length of Inokashira Ave., which runs from Inokashira park in Kichijoji, to Yoyogi park in Harajuku. I always recommend this course for bikers and walkers alike, because it gives you a great idea of the distinct environments of Tokyo suburbia and the downtown area. It becomes increasingly "downtown" as you approach Harajuku, and a great way to finish off the trip is over in Shibuya with some food and drinks. The course at a leisurely pace shouldn't take more than 2 hours, although it's fun to stray a bit off the main road Inokashira Ave., and see some of the neighborhood environments.