May 2022: The line was extended from Front Populaire to Mairie d'Aubervilliers. Route Line 12 is long and completely underground. It is, by design, a particularly twisting route with multiple corners and steep climbs. Beginning at Issy-les-Moulineaux, south-west of Paris, with a three way tunnel underneath l'avenue Victor-Cresson, the terminus is at Mairie d'Issy, and has only two tracks. It runs north-east, entering Paris at Porte de Versailles, a major station with three tracks, one of which gives access to the workshop at Vaugirard. The line then runs underneath rue de Vaugirard, following all the bends of this narrow street. After Falguière, the line veers back south-east in a radius bend underneath the boulevard du Montparnasse. It connects with line 13 at Montparnasse – Bienvenüe, and exit leads toward the Tour Montparnasse. Before the station, a two-way tunnel branches right (i.e., south), the beginning of a planned branch line to la Porte de Vanves (which later became line C of the Nord-Sud Company). This branch was in turn integrated into the original line 14 of the Métropolitain system, and became a part of line 13 when 13 and 14 were joined at the Seine. The Vanves branch now serves as a depot and workshop. After the junction with Line 4 at Montparnasse – Bienvenüe, Line 12 goes north-west underneath the Boulevard du Raspail; at long. After the Rue du Bac station, it runs north underneath the Boulevard Saint-Germain until the river Seine, under which it (and the tunnel of RER Line C) passes via a 4 per cent descent and 3.5 per cent climb, to reappear on the Right Bank. After Concorde, the tunnel burrows below that of Line 1, then follows a twisting route through Rue Saint Florentin, then Rue du Chevalier-de-Saint-George and finally Rue Duphot before reaching Madeleine, named after the Église de la Madeleine, where the bend necessitates curved platforms. The route also goes underneath the tunnel of the new Line 14, and twists north underneath Rue Tronchet. After intersecting with Line 13, it reaches Saint-Lazare by a curve with a radius of just , turning east under Rue Saint-Lazare. Between the Trinité station and the Notre-Dame-de-Lorette station the tunnel has three lines, including a central one which connects the two at the exit of Trinité. This extra track was used for a long time to move the trains of Line 13 from the Vaugirard workshop back