El Castillo has four sides, each with 91 stairs and facing a cardinal direction; when the stairs on the top platform are included, this becomes a total of 365 steps. As all of us know, it is the number of days in the solar year that we find here in this entire structure. The shadows cast by the setting sun on the spring and fall equinoxes resemble a snake curving down the stairs. Image by Slovenčina/Walkerssk of Pixabay.