The New Lyon-Turin Line (NLTL) is an essential component of the “Mediterranean Corridor”, one of the nine TEN-T network corridors, the future “European metropolitan railway” that will promote the movement of people and goods by rail, an ecological mode of transport. The goal is to reduce road transport, which increases pollution and greenhouse gas emissions. The core element of the new line is the 57.5 km Mont Cenis Base Tunnel. The reference geological model is based on the data obtained during the excavation of the inclined access adits at Saint-Martin-La-Porte, La Praz and Modane, including the La Maddalena exploratory tunnel. With the planned investigations completed, all the collected data will allow a technical and economical optimization of the construction phase and operation and maintenance of the line. The impact on water resources is minimized by using a full-round waterproofing system up to a hydrostatic pressure of 10 bar. The expected residual water flows at the portals will be exploited for both drinking water and heating purposes. With 12 % of the tunnels already excavated, there are currently 800 people working on the NLTL. This unique project, with its extraordinary history and innovative features, has been proposed as the subject of an international case study.