Notre Dame Cathedral sits on an island in the Seine river in Paris, known for its flying buttresses. It is considered the official center of Paris. Saint Denis was the bishop of Paris in the 3rd century who was executed while still preaching. The Louvre was originally a royal palace and now houses a huge collection of art from around the world, entered through a modern glass pyramid built below ground level. The Eiffel Tower is more impressive in person than in photos, with restaurants and views from upper levels. Versailles outside Paris exemplified the lavish spending that contributed to the French Revolution, with real gold thread in the king's bedroom. Napoleon is entombed at the Invalides in Paris.