"In Otay Mesa, the soil is soft enough to be dug by hand, yet firm enough so that the tunnel walls can often stand without wood or concrete reinforcement," Reel reported for The New Yorker.
A tunnel connected to the Altiplano Federal Penitentiary and used by drug lord Joaquin "El Chapo" Guzman to escape is seen in Almoloya de Juarez, on the outskirts of Mexico City, July 15, 2015.