The city was not as large as Teotihuacan, but it was still immense. El Castillo, measuring 180 feet on its base and 78 feet tall, dominates the complex. Each of its four sides has 91 steps, and when added together with the temple on top, equal to 365, which is also the number of days of the Mayan calendar. During the equinox, the setting sun would cast a shadow on the steps that would give the illusion that a snake - the god Kukulkan - is descending from the temple. Another fascinating thing about the pyramid's steps is that when you stand in front and clap, the sound will bounce all the way to the top and echo back as different sound - something similar to a chirp of a quetzal bird.We stood in front of the pyramid doing this. The acoustics of the building was also designed such that the priests from ancient times can stand on top of the pyramid and can still be heard by the people below. The guide said that classical singer Placido Domingo did a concert in Chichen Itza, singing on top of the pyramid without using any sound system, and still be heard perfectly by the concert-goers.