Just got back from three glorious days cycle touring in Izu with friends. When I get time I will log our route on Gmaps pedometer (a fantastic site), and maybe upload some photos.
Basically we took trains (including Shinkansen) to a town called Numazu, the gateway to the west coast of Izu. From there we rode south along the west coast, staying at a town called Toi, and then riding all the way around the point to Shimoda, staying at a small place by the beach just south of Shimoda. Fantastic trip - narrow coastal roads, scenic, very few cars, traditional towns. We rested one day on the beach in Shimoda then I bagged my bike again and caught train home from there. The others took the boat down to Niijima island for the rest of the Golden Week holiday.
Highly recommended, not least because it is pretty difficult to get lost along the coast - just keep the ocean on your RHS ! (except on the switchbacks - many hills - not a course for the faint hearted.)