The maritime town of Cherbourg boasts the largest manmade harbour of Europe, covering a massive 1,500ha/3,700 acres. With three dikes, it stretches for over 6km/4mi and has three main forts. Construction began in 1738 and lasted for 70 years! At the time, this major building projects was sparked by a desire to defend the French coastline. A national monument, still standing despite battles and wars, it is best explored on a boat trip.