If you want to take a quick and pleasant afternoon trip from Portland, hop aboard the ferry to Peaks Island. Only 15 minutes from Potland, the Island is about 4 miles around and worth a nice walk or bike ride. You can rent bikes there too. Charming and peaceful. There is a small beach only a few minutes walk from the ferry and a few restaurants there too. If you get the urge to stay, there is a nice B&B and a beautiful Inn. Check it out. You'll come back for sure.