Salk Institute for Biological Studies (1962) by Louis Kahn- La Jolla. The plaza was designed in collaboration with Mexican architect Luis Barragan. Kahn invited Barragan to the project after seeing his work at MoMA in New York. Barragan suggested the plaza should consist of a single water feature, free of plant life and dirt.
The design also includes a feature where the twice a year equinox sunset lines up perfectly with the channel.
Apparently, it's not a secret.
The clouds weren't cooperating, but the sun did peep through for a bit and sure enough, it lined up exactly with the channel.
More on the Salk, here.