The historic Petite Ceinture, the small rail line that used to circle Paris, is finally to become the nature trail that local activists have been lobbying for. Take a tour with Association Espaces this weekend (April 3 and 4) from Porte de Versailles to Porte de Sèvres at 2pm, 3:30pm, and 5pm. IMPORTANT: to take the tour you’ll have to sign up on Wednesday the 30th at the Espaces stand on the Parvis du Mairie du XVe arrondissement, from 10am-6pm. On the plus side, it’s free. You can also take a virtual tour of the Petite Ceinture and its 200 species of flora and fauna (not just rats and pigeons, go figure).