The Cathedral of St Etienne, or St. Stephen of Sens is one of the oldest Gothic buildings in France, its construcition having been started in 1140, though it would not be finished for nearly 400 years. Like all Gothic churches, the Cathedral of St. Stephen is built in a cruciform shape; past the transept (the "cross-piece" in the cruciform shape) is the choir, the design of which influenced the design of the choir of the Canterbury Cathedral.
St. Stephen's is a remarkable church for both its adornments and its place in medieval Christian history. Its western front continues many sculptures in three portals. These sculptures and statuary depict Biblical scenes that include the Parable of the Ten Versions, St. Stephen's martyrdom and the story of John the Baptist, as well as statues commemorating the church's benefactors.
Beyond its decorative elements, however, is its treasury. Charlemagne himself brought an alleged piece of the True Cross here for safekeeping; the treasury also contains the vestments of Thomas Becket, and it is now a museum. You will also find the tomb of Louis, Dauphin of France, the son of Louis XV who died at the age of 36. Curiously, his heart is buried in the Basilica of St Denis.
Sens is a small commune; in France, this is analogous to a township or similarly small, incorporated municipality. While the Cathedral is the main site, you will also want to visit Serres municipales de Sens, municipal gardens found in the Parc du Moulin. Open every afternoon, these botanical gardens have three different rooms displaying flora divided into cacti, epiphytes (carnivorous plants, orchids and their relatives) and a winter garden, containing a tropical forest.