A favorite local activity is pedaling the 30-mile loop around Lopez Island. Once you get beyond the steep initial climb from the ferry dock, the rest of the island consists of gently rolling hills, perfect conditions for families.
Mountain bike rentals and tours are available from Lopez Bicycle Works (360/468-2847, www.lopezbicycleworks.com [1], 10 a.m.–5 p.m. daily Sept.–May, 10 a.m.–6 p.m. daily Jun.–Aug.), along Fisherman Bay just south of Lopez Village, both of which will deliver rental bikes to you at the ferry terminal or your lodging place for a small fee. Be sure to call ahead, as the owners are sometimes not in the shop during posted hours. Cycle San Juans (360/468-3251) guides bike tours around Lopez.
Links:
[1] http://www.lopezbicycleworks.com