Important landmarks of Greater Mexico City include the Historic Center of Mexico City, the floating gardens of Xochimilco, the Pre-Hispanic city ruins Teotihuacan, located at the municipality of the same name, all three declared World Heritage sites by UNESCO in 1987. The National Parks at the southern portion of the Federal District (over the mountainous range of Ajusco), the Parks of Popocatépetl and Iztaccíhuatl and the National Reserve of Lake Texcoco are some of the environmental landmarks of the valley as well.