The outer walls of the citadel are among the most dramatic in all of pre-Columbian South America, reaching 20 metres high in places and stretching nearly 600 metres in length. Three deliberately narrow entrance passages — so narrow that visitors must turn sideways — were designed to prevent easy assault. Walk the perimeter for sweeping views over the cloud forest canopy and the deep Utcubamba Valley far below. Inside, the density of structures gives a real sense of the city as it once was.