On March 19, thousands of people will visit this pyramid in Mexico. As the sun starts to set, they’ll see a streak of light in the shape of a snake. It will “slither” down the pyramid!

The snake can be seen only twice a year—on the first day of both spring and fall. On those two days, the sun shines on the pyramid’s steps in a special way. The pyramid was built long ago by people known as the Maya in a city called Chichén Itzá (chee-CHEN eet-SAH).