Nearly 5,000 feet long, with pipes and fluorescent lights, carved deep into the earth. That's the tunnel where Mexico's most-wanted drug lord fled in a daring escape earlier this month from a maximum-security prison.

Joaquín Guzmán Loera, known as El Chapo and head of the violent Sinaloa cartel, is still at large. While much of how he escaped is still a mystery, one thing is known: It was the tunnel that carried him to freedom.

The Sinaloa cartel has pioneered the use of tunnels to smuggle drugs, equipment and even people across the border.

Reporter Monte Reel has written about the tunnels for the New Yorker, and joined the show for more.