Chichen Itza is one of the best preserved ruins in Yucatan peninsula. It belongs to the post classic period of Mayan history (9-10th century AD). Hence, the place has enough influences from Mayan and Toltec cultures. Toltecs from central Mexico seem to have had quite a significant impact on the Mayan way of life towards the early part of second millennium AD. You can see Chaac-Mool (Mayan rain God) living in perfect harmony with Kukulcan (Mayan version of the Toltec God, Quetzalcoatl). Toltecs also brought the bloody ritual of human sacrifice which seems to have been followed quite religiously in Chichen Itza. Some relief depicting the gory scenes are quite disturbing.
The best restored of its structures is El Castillo (the castle). Like a moth catcher attracting the flies, the building pulls around 50% of the visitor population at any given time leaving the rest of the ruins like what it should be - desolate and peaceful.
El castillo is a culmination of Mayan obsession with the calendar. The pyramid has 91 steps on each of its four sides. They along with the platform on top make exactly 365 steps - the number of days in a solar year. During equinoxes, the steps (apparently) cast a shadow that gives an impression of a giant snake crawling up and down the sides of the stairway. If you have low tolerance to dirt, smell, sweat and long queues you can even take the dark, damp claustrophobic steps inside the pyramid leading to an old jaguar throne and a sacrificial platform.
Behind the pyramid is an unique Templo de los Guerreros (temple of the warriors) and the Grupo de mil Columnas (group of 1000 columns) - resembling a miniaturised hypostyle halls of Egyptian temples. Chichen Itza also houses one of the best restored and biggest ball court in the peninsula. Churchill's comment that golf involves putting an uncontrollable ball through an inaccessible hole with equipment ill adapted for the purpose fits the Mayan ball game better. Apparently, the losers of the game used to be sacrificed to the Gods. Looking at the size and location of the hole and considering that arms and hands are out of bounds, I think most games would have ended in a draw without any losers. As the player's union got stronger, the goal posts could have climbed higher!
Other worthwhile stopovers include Tumba del Gran Sacerdote (tomb of the grand priest), El Caracol (the "snail" - an ancient Mayan observatory), El Mercadao (the market - home to the tallest columns) and La Iglesia (the "church" - structure with one of the best preserved carvings in the entire site).