@fbaezer,
The hidden wonder is called El Cárcamo.
The idea was to integrate public art to a functional building.
It is built over a chamber of the early XX Century that distributes water from the rivers Cutzamala and Lerma to Mexico City.
The ensamble, made in 1951, reunites hidraulic and civil engineering, public architecture and mural art by Diego Rivera. Art and science get together in the benefit of society.
In the front, a statue of Tláloc in the water, made by Rivera
In the inside, a mural by Rivera (creationists, beware!): "Water and the origin of life". On the lower levels, microscopic creatures; in the middle levels, sea and river life; on the higher levels, humans, and people receiving water in the pipes. On the balcony, the engineers and scientists that designed the water system: