The most photographed lighthouse on the East Coast stands on a rocky headland in Cape Elizabeth, about fifteen minutes south of downtown. The white tower and red-roofed keeper's house against dark cliffs and Atlantic surf are exactly the postcard Maine you came for — particularly at sunrise.
The surrounding Fort Williams Park is free, opens early, and has good cliff-side trails, picnic lawns, and the remains of a coastal artillery fort. Park outside the gates on summer weekends and walk in to skip the queue.