Buttes Chaumont, one of the largest green spaces in the city, boasts landscaped slopes that hide grottoes, waterfalls, a lake, and even an island topped with a temple to Sibylle. What was once a gypsum quarry and rubbish dump was transformed by Baron Haussmann in time for the opening of the 1867 Exposition Universelle. Furthermore, the park features the tracks of the former Petite Ceinture railway which once encircled Paris.