Marstal is the second city -- really, an overgrown town of 2,500 people -- standing at the eastern end of the island. Its marina is busy in summer with yachts, and there's even a shipyard, but its glory days are long gone. Back in the 1800s, as many as 300 merchant ships called Marstal their home port.
The harbor is protected by a granite jetty, forming one of Denmark's largest yacht basins. It's idyllic for all with nautical interests, but if you have time for only one town on Ærø, make it Ærøskøbing. Otherwise, wander the streets of Marstal for an hour or two, the names of which still evoke the town's seafaring past -- Skonnertvej, Barkvej, and Galeasevej (Schooner, Bark, and Ketch roads).