This open air museum is an extensive site mixing Napoleonic structures with Kriegsmarine bunkers. The original French fort was completed in 1879 and you can still walk through the original buildings, along with many German constructions from WW2.
Known as Stp221 Arnika Fort de La Crèche, the position was created to protect the port of Boulogne and was the scene of fierce battles during WW2, eventually being secured on September 22, 1944, by the Queen’s Own Rifles Regiment of Canada - to whom there is a memorial on site.
Cared for by an amazing group of volunteers, Fort de la Creche is open for visitors on a few days each month during the summer and it’s well worth the time to walk around. A guide is often on hand to give you background to the location and its history but there are also information boards at the different locations around the site.