The islands of Casco Bay are also known as the Calendar Islands because an early explorer mistakenly thought there was one for each day of the year (in reality there are only some 140). These islands range from ledges visible only at low tide to populous Peaks Island, a suburb of Portland. Some are uninhabited; others support year-round communities as well as stores and restaurants. Fort Gorges commands Hog Island Ledge,
and Eagle Island is the site of Arctic explorer Admiral Robert Peary's home. The brightly painted ferries of Casco Bay Lines are the islands' lifeline. There is frequent service to the most populated ones, including Peaks, Long, Little Diamond, and Great Diamond.
There is little in the way of overnight lodging on the islands; the population swells during the warmer months due to summer residents. There are few restaurants or organized attractions other than the natural beauty of the islands themselves. Meandering about by bike or on foot is a good way to explore on a day trip.