paris métro line 10 (french: "ligne 10 du métro de paris") is one of the sixteen lines of the paris métro. it links boulogne – pont de saint-cloud in boulogne-billancourt in the southwest with gare d'austerlitz in the southeast, travelling under the neighbourhoods situated on the rive gauche, in the southern half of paris. the line is entirely underground and stretches across 23 stations. it has the least traffic of any of the fourteen main métro lines (excluding line 3bis and line 7bis).