The dominant edifice of Chichen Itza, the iconic pyramid, was called El Castillo by the Spanish, who thought it might be a fortress.
In truth El Castillo is a monumental representation of the Mayan calendar.
There are 18 terraces on each side, the number of months in the Mayan year.
There are four staircases, each with 91 steps, with one final step to the summit temple making 365 steps, one for each day of the year.
But to see the most impressive aspect of the pyramid, you need to join the tens of thousands visiting on the spring and autumn equinoxes.
On these days, the afternoon sun picks out the serpents carved into the staircase, which “moves” by a celestial trick of the light.
It is a magnificent testament to the astronomical and architectural genius of its construction nearly 1,000 years ago. If you can’t make the equinoxes, a sound and light show in the evenings offers an approximation.