At the fall of Teotihuacán the mountains in the central plateau saw the construction of several city-states protected by walls, including Xochicalco, one of the most dynamic. It stands on top of a levelled hill at the crossroads of several trade routes. In addition to its elegant Feathered Serpent Temple and its enchanting setting, Xochicalco (the “place of the house of flowers”) is famous for its underground astronomical observatory (in a cave), one of the best preserved in Mesoamerica.