The Île du Louvre occupies the threshold between the Louvre and the Seine, transforming the ground below it into a civic museum of water. Instead of adding another object to Paris’s monumental skyline, the project works through excavation: enclosed museum rooms are set within a continuous public hall. The central space is entered directly from the city and operates independently as an urban commons, while the rooms connect at the upper level to the Louvre’s museum circuit. Water is made visible through roof channels, light wells, pools and sediment chambers, becoming exhibit, atmosphere and environmental system at once. Each room stages a different encounter with the Seine — its sound, memory, material traces and changing levels. Linking palace, river and city without competing with the historic monument, the project reframes the museum as living infrastructure: a place where water is not represented, but experienced.