The easiest way to extend your trip would be to detour a bit west from Okayama and visit Kurashiki, Okayama's premier tourist city. This is particularly easy if you’ve chosen to cycle from Ushimado through central Okayama; it’s only about 15km away from the city center and you’ll be cycling more or less in that direction anyway (you would just veer a bit to the south). Like most tourist cities in Japan, only a tiny area has been preserved (the rest is a fairly typical modern city) but that area, with its canals and storehouses, is very nice indeed... and mobbed with tourists year-round.