Besides the numerous churches and castles, there are six large cathedrals in Picardy. At 145 metres long, the cathedral of Amiens is the largest in France. The Gothic era, in particular, left a mark on Picardy; Notre Dame of Laon is a good example of this. The Basilica of St. Quentin is also interesting from an architectural point of view. At the Château-fort de Guise you can visit some terrifying oubliettes ("secret dungeons reached only via trapdoor"). The Renaissance Castle of François I in Villers-Cotterets is known for its elegant park. The St. Michel Abbey in Thiérache is also an important building in the region.