Police in the United States have shut down a 360ft (120 metre) drug-smuggling tunnel under the US-Canadian border.
The tunnel was equipped with ventilation and a cart
Three men from the province of British Columbia in Canada were arrested in the US and charged with drugs offences.
The tunnel, which emerged in the living room of an abandoned home on the US side, is the first to be discovered along the US-Canada border.
It was only used briefly to smuggle marijuana, police say, but would also have been used to move people and guns.
Drugs gangs from British Columbia smuggle millions of dollars' worth of Canadian marijuana to the US every year.
The tunnel runs from a large metal shed in Langley in Canada to a home in Lynden, Washington, in the US.
Canadian customs officials became suspicious when they saw a lot of wood and iron disappearing into the shed in February.
They alerted US officials, who installed secret cameras and microphones.
Francis Devandra Raj, 30, who owned the hut in Langley, Timothy Woo, 34, and Jonathan Valenzuela, 27, were arrested soon after they began to use the tunnel.
The tunnel, which was equipped with lights and ventilation, is thought to have taken about a year to construct. It was lined with wood and reinforced with concrete and metal. A small cart had also been installed to move goods and people.
"It was well built, probably one of the most sophisticated tunnels we've ever seen," said Rod Benson, of the US Drug Enforcement Administration.
Neighbours said that despite the scale of the construction work, their suspicions were not aroused.
"I'm a kind of nosey person... and I have never seen any activity to speak of," Mike Hamm, who lives near the tunnel's Canadian entrance, was quoted by Reuters as saying.
The owner of the property on the US side has not been detained, but police say they are still investigating.
More than 30 tunnels have been discovered running from the US across the border to Mexico.