There certainly are other ways to while away a summer day in Greater Portland, but you’d be hard-pressed to find a better experience than island-hopping aboard a Casco Bay Lines ferry. Sure, you can simply ride out to an island for a look-about and return, or enjoy a sunrise, sunset, or moonlight cruise. But for a real immersion, consider the Mailboat Run. You’ll be among islanders, visitors, pets, and freight to-ing and fro-ing between Little Diamond, Great Diamond, Long, Cliff, and Chebeague islands. The 2½-to-3½-hour working cruise is offered twice daily year-round; bring your own picnic lunch on the morning run or snacks for the afternoon one.