A tunnel found running under the U.S.-Mexico border near Jacume, Mexico had solar-powered electrical, lighting and ventilation systems, according to the U.S. Border Patrol.
The tunnel also contained a sump pump system to remove excess water and a rail system that ran its entire 627 feet.
Mexican authorities discovered the tunnel on September 19, 2018.
Border Patrol said the tunnel extended 336 feet into the U.S., but didn't have a exit point in the country. Agents found an exit shaft that reached 15 feet towards the surface, but didn't break through.
The entrance to the tunnel was about 220 feet south of the border.