Tijuana, Mexico (CNN) - The Mexican military offered a rare look inside a sophisticated drug tunnel.
The entrance is in a building in a busy business park in Tijuana, just four blocks from the border.
An elevator inside a closet goes down to the tunnel, which is nearly four football fields long.
It was found after people reported suspicious activity back in February.
17 people were arrested in a raid.
The tunnel includes an elevator, electricity and lights, ventilation and a rail system.
It could have generated millions for the cartel building it.
But it was shut down before it was completed.
It would have come out somewhere in San Diego.
A Mexican reporter says there's a good chance it would have gone to another warehouse.