The history in a 120-year-old building is priceless. Or in the case of an old, Victorian-style theater in London, about £40 million ($51 million).

That’s because police there recently made a stunning discovery: in the bowels of the 750-seat Broadway Theatre, authorities uncovered a massive (and lucrative) cannabis farm.

Both Metro and the Mail Online reported that London police believe that the weed factory had been in operation for about a decade, and that those running it likely cleared £4 million ($5.1 million) a year.

The discovery of the farm might be as incredible as the existence of the farm itself. Responding to a break-in at a house located near the theater, police noticed that the floor of one of the bathrooms was hollow. From there, they discovered a tunnel leading from the bathroom to a car park—and in the direction of the old theater’s abandoned basement.

Originally built in 1897, the Broadway Theatre was converted into a shopping center about 50 years ago. The basement housing the marijuana farm could not be accessed from the shops above, making it a choice hideout for the criminal operation.

Neighbors Became Concerned

In a statement reported by Metro, a spokesperson for London police described the bust: “On October 1, officers were called to an address following reports of a disturbance. They discovered a large number of cannabis plants along with equipment used in the cultivation of cannabis in an area beneath the residential properties. Three men, aged 28, 45, and 47, and a 36-year-old woman have been arrested on suspicion of the cultivation of cannabis. They have all been released under investigation.”

A man who lived next door to the house where the tunnel originated told Mail Online that he and his wife “sometimes heard what seemed like drilling.”

“It was never for very long but it vibrated the walls upstairs,” he said. “We had no idea what it was, we just thought it was some building work nearby – it’s a busy road.”

The October visit marked the third trip by London police to the house. The neighbor said police were called in August and in September after mysterious men tried to enter adjacent properties, including once attempting to kick in the door. It wasn’t until police were again dispatched on October 1 after yet another report of an attempted break-in that the extraordinary discovery was made.

“To think this has been happening next to us for ten years without any of us noticing is certainly surprising. I was shocked,” the neighbor said.

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