This Platform of Venus is dedicated to the planet Venus. In its interior archaeologists discovered a collection of large cones carved out of stone, the purpose of which is unknown. This platform is located north of El Castillo, between it and the Cenote Sagrado. Chichen Itza was one of the largest Maya cities, with the relatively densely clustered architecture of the site core covering an area of at least 5 square kilometres (1.9 sq mi). Smaller scale residential architecture extends for an unknown distance beyond this. The city was built upon broken terrain, which was artificially levelled in order to build the major architectural groups, with the greatest effort being expended in the levelling of the areas for the Castillo pyramid, and the Las Monjas, Osario and Main Southwest groups. The site contains many fine stone buildings in various states of preservation, and many have been restored. The buildings were connected by a dense network of paved causeways, called sacbeob.Archaeologists have identified over 80 sacbeob criss-crossing the site, and extending in all directions from the city. The architecture encompasses a number of styles, including the Puuc and Chenes styles of the northern Yucatán Peninsula. The buildings of Chichen Itza are grouped in a series of architectonic sets, and each set was at one time separated from the other by a series of low walls. The three best known of these complexes are the Great North Platform, which includes the monuments of El Castillo, Temple of Warriors and the Great Ball Court; The Osario Group, which includes the pyramid of the same name as well as the Temple of Xtoloc; and the Central Group, which includes the Caracol, Las Monjas, and Akab Dzib. South of Las Monjas, in an area known as Chichén Viejo (Old Chichén) and only open to archaeologists, are several other complexes, such as the Group of the Initial Series, Group of the Lintels, and Group of the Old Castle.