Another tunnel used for smuggling drugs across the U.S.-Mexico border has been discovered, this one by Mexico’s Ministry of National Defence.

The tunnel, which stretches about 755 feet and goes as far as 59 feet under the surface, ran from the Mexican state of Sonora to San Luis, Arizona.

On the Arizona end, the tunnel opened up in an unopened business. On the other end, the tunnel opened in San Luis Rio Colorado, in Sonora.

With a height of just over four feet, the tunnel had electricity for lights, ventilation, and was wide enough to push drug-filled carts under the border.

Authorities are still trying to determine who was using and who constructed the tunnel.

This is the 22 tunnel of this kind found in the last three years. Underground passages have become increasingly popular in recent years as border security has become much tighter.