GY1 6JN, Guernsey
Castle CornetNo one approaching St. Peter Port from the sea can miss 13th-century Castle Cornet, perched on an island at the edge of the harbor. Its surprisingly large interior is beautifully preserved and well worth the entrance fee, which includes an optional guided tour and access to its five museums and four gardens. Try to arrive by noon, when costumed soldiers fire the cannon. As in the town generally, there are steps and uneven ground to contend with.