When the sunlight bathes the Kukulcán Pyramid in the Mayan city of Chichén-Itzá during the equinox sunset, it casts seven triangles of light and shadow that creep downwards along its northeast stairway. According to the Popol Vuh, the effect can be interpreted as the myth of the gods of the Heart of Sky coming to the Sovereign Plumed Serpent. Unfortunately, neither the event nor the kind of geometry used to build the pyramid is reported in the extant Mayan codices. There are two reliable facts: first, a line across the pyramid’s base coincides with the orientation of the summer-winter solstice; second, an earlier, smaller pyramid is concealed beneath the current one. Hence the major question here is whether the light and shadow effect was intended or occurs accidentally. Perspective as a surveying method for building provides a key to this riddle, because it accounts for a line according to which the Kukulcán Pyramid was built. To tell the history of this line, we have to bring into context other sunlight effects that take place across the Mayan area, taking into account the question of how the buildings in which such effects occur were built.