Fort Prins Frederik, near Ooltgensplaat, used to be part of the Defense Line of the Hollandsch Diep. Originally it was a French fort built in 1809. It was then named "Fort Duquesne" after a French general. Four years later, Dutch soldiers managed to get hold of the fort. Since then, the building is better known as "Fort Prins Frederik". The building still exudes the adventure and furiosity it used to have. You can see a number of gun openings in the facades. Since the fort was also used as an observation tower, it has a flat roof.
The area around the fort is an excellent place to relax away from the crowds.
