The line C platforms run parallel to the Seine at just above river level and are provided by natural light through 28 large windows that are designed to withstand flooding from the river. The line B platforms pass underneath the Seine and are at right-angles under the RER C platforms.[2][3]
The RER line C section of the station dates back to 1900, when it opened as the Pont Saint-Michel station on the extension of the Compagnie du chemin de fer de Paris à Orléans from the Gare d'Austerlitz to a new terminus at the Gare d'Orsay. The Pont Saint-Michel station was built under the quays of the Seine, almost at river level, and its constrained location, with narrow and low platforms and reverse curves, affects operations to this day. Originally the platforms were lit by openings in the river bank, but these were filled in after the station was inundated during the Seine floods of 1910.[citation needed]
In September 1979, a 1 kilometre (0.62 mi) tunnel was constructed to link the Gare d'Orsay (now the Musée d'Orsay) to Invalides thus creating a cross-city line initially called the Transversal Rive Gauche. At the same time, the Pont Saint-Michel station was slightly widened. In May 1980, the Transversal Rive Gauche became the core part of the new RER line C.[citation needed]
The RER line B had passed under Pont Saint-Michel station since December 1977, but the location under the quays made the construction of an interchange difficult. In February 1988, the line B platforms were finally opened, and the station was renamed to Saint-Michel–Notre-Dame. At the same time, Cluny–La Sorbonne station on the metro, which had closed in 1939, was reopened to connect with the new RER station and give access to Boulevard Saint-Germain.[citation needed]
In August 2022, the line C platforms were closed for modernisation. Originally intended to be complete by December of the same year, the platforms eventually reopened in April 2023. The principal improvement was the reinstatement of natural lighting by replacing the original openings, closed in 1910, with 28 large windows that are designed to withstand flooding. Other improvements were the provision of improved ventilation and escalator access.[3][5][6]
