I've done an organized ride on Lopez Island which was throughly enjoyable. It was 37 miles or so (you can find a map here: http://www.seattlebiketours.org/memb...ashington.html ). I think they advertised the island as relatively flat as compared to the others, but I recall thinkin' it was pretty durn hilly. There's also a map for a loop of San Juan Island on the link. They list it as rolling to hilly. someone once told me that the islands are actally mountains partly under the water, so no wonder it's hilly! You also have to be very careful about reading the ferry time tables correctly. Shaw Island, for instance, has no hotels or restaurants, so if you miss the last ferry or get on the wrong one, you are stuck sleeping on the dock.