La Dune du Pilat is the biggest dune in Europe and is an aeolian dune that progrades towards the continent. The sand comes from the banks in the ocean and is filtered through a layer of peat at the base of the dune. This layer contains compressed pine trees and cones that turn into oil over time. The fresh water from rains is filtered through the dune and comes out at the beach. It is a unique geological wonder worth visiting.