The island's most scenic route is Osado Skyline Drive, which snakes across the mountains from Ryotsu to Aikawa. You must take either a tour bus from Ryotsu or a taxi from Aikawa to Chikuse, where you can catch a bus for the return trip. (You can do the route in reverse as well.) It's particularly beautiful in autum foliage season.
Sado Skyline Rd., Sado-shi, Niigata-ken, Japan