I have been coming up to Lopez since a little kid and my family has a house/business up there. I am not able to come up as often as I used to (or like to) but one essential To-Do is always to go on a bike ride around the island.
Lopez is a great biking island for individuals, groups or families (safety is not as much of a concern with little children most other areas). If you are a boater, this is an excellent day trip or use of transportation to other places in the island such as the local shops in the Village or the variety of great parks. The island is relatively flat besides the initial climb off the ferry and the best biking island in the San Juans.
There is just something about biking on Lopez, the scenery, smells and friendliness of the people just melt the stress away. Lopez tends to stick with you and you have no choice but to be back.