SAN LUIS, Ariz. (KXAN/CNN) — Underneath a defunct Kentucky Fried Chicken shop in San Luis, Arizona, federal authorities made a startling discovery — a tunnel to Mexico.

The Department of Homeland Security and the U.S. Customs and Border Protection recently obtained a search warrant for the former restaurant and inside they found a tunnel in the kitchen area.

The tunnel was only 8 inches in diameter but was 22 feet deep and nearly 600 feet long, connecting the fast food location to a home in Mexico. 

Authorities say the tunnel was used to smuggle illegal drugs across the border.