Searching for dark matter in the Homestake Gold Mine
In the 1960s scientist Ray Davis arranged to set up a small lab in the Homestake Gold Mine in Lead, South Dakota.
Davis created a detector and installed it in one of the mine's caverns, more than 4,800 ft (1,463m) under the earth. He used the device as a way to detect and measure neutrinos, or tiny subatomic particles.
At first, his calculations were considered way too large to be accurate. But his figures stood up to scrutiny over time, and in 2002 Davis was awarded the Nobel Prize for physics.
Almost 50 years later, modern scientists are trying to build on Davis' early work - only this time, they're constructing an entire facility on the spot where he once eked out a lab.
The Sanford Underground Research Facility is being built where the gold mine once operated, and scientists there hope to shed more light on the hypothetical particles described as the building blocks of the universe.
The BBC's Kate Dailey was given an exclusive tour of the mine as it prepares for two major scientific experiments.
Produced by the BBC's Matt Danzico