TSIL436 = The Secret in Locker 436
In January 2020 authorities uncovered a cross-border tunnel that stretches more than three-quarters of a mile (4,309 feet). That’s the longest of its kind ever discovered along the Southwest border, per the U.S. Border Patrol.
It starts in Tijuana, in an industrial area near the Otay Mesa Port of Entry. It ends in California, in the Otay Mesa warehouse district in San Diego, where agents found hundreds of sandbags blocking what they suspect was the exit. An offshoot from the main tunnel ended without breaching the surface.
Good video summary here–