El Castillo’s hidden pyramid, Chichén Itzá, Mexico, 2016
With its 365 magnificent steps and imposing height, the four-sided El Castillo pyramid (or the Temple of Kukulkan) is one of Mexico’s biggest tourist draws.
And, in 2016, archaeologists discovered it was hiding a secret. Already aware that a second pyramid lay hidden inside El Castillo’s walls, experts performed scanning techniques and revealed a third.