Chanteloube viaduct - 13km

The Chanteloube Viaduct was the start of the Ubaye railway line, which was to link Chorges to Barcelonnette.
Construction of the line began in 1909 but was interrupted in 1935. The viaduct was never put into service.
When the Serre-Ponçon dam was built, the highest point (780 metres) was exactly at the height of the viaduct's eastern fore-deck. 
The viaduct was therefore completely submerged in 1961 when the lake was impounded, but it reappears, at least in part, above the water whenever the water level drops.