Unearthed: The drug tunnel under US-Mexico border

The structure was engineered with wooden beams plywood wall, ceiling and floor panels (Getty Images)

Like many a property investment, it must have seemed like a good idea at the time: for just $1.5m, the creators of the discrete new-build, which came with air-conditioning and fully installed electrics, expected to gain instant ownership of one of the world's most valuable pieces of commercial real estate.

Then disaster struck. Authorities in San Luis, a border town in the south-west corner of Arizona, arrested a man found with 39lb of methamphetamine in his car. When they searched the mall he'd emerged from, they stumbled upon the illicit construction: a 240-yard tunnel which led to an ice plant across the border in Mexico.

The structure was engineered with wooden beams, plywood wall, ceiling and floor panels. Its entrance was hidden by a water tank. Running 55 feet under the surface of the soil, it was designed to ship vast quantities of drugs.

"It's really a piece of work," said Douglas Coleman, a US Drug Enforcement Administration agent, who estimated that the tunnel cost $1.5m to build. "You would need someone with engineering expertise to put something together like this."