The tunnel (Photo: Policia Federal)

Among all the illegal tunnels in the world, the one found this week by U.S. and Mexican law enforcement agents is a doozy. It’s 2,600 feet long, about three feet wide, and equipped with a rail system to move large quantities of drugs.

Which the agents also found: 10 tons of marijuana, in 873 packages.

The tunnel, which crosses the border in Otay Mesa, a San Diego neighborhood just across the border from Tijuana, was controlled by El Chapo, the famous Mexican cartel boss. According to the San Diego Union-Tribune, agents discovered it in a sting operation. On the U.S. side, agents found a small opening that dropped 32 feet down, and their Mexican counterparts found a similar entrance on the other side.

The only real way to locate tunnels like these is through law enforcement action: tunnel detection technology is neither accurate or flexible enough for tunnel hunters to rely on. Which is one reason why drug cartels keep building them: they’re really, really hard to find.

Bonus finds: Half-male, half-female butterfly; coffin of a dog

Every day, we highlight one newly lost or found object, curiosity or wonder. Discover something unusual or amazing? Tell us about it! Send your finds to sarah.laskow@atlasobscura.com.