The Boulby mine is located more than 1,400 metres – nearly a mile – underground.

Its tunnels are humid and reach temperatures of up to 40C. It's from here that Britain gets much of its potash, the potassium-rich salt used in fertiliser.  

Boulby is the second-deepest mine in Europe, but it's not the only thing that sets it apart – its tunnels extend several kilometres out to sea.

Here, miners work to get the ore needed to help Britain grow its food, deep below and far from shore.

Watch the short video above, from the BBC programme Britain Beneath Your Feet, to see what it's like to work both underground and under the sea.

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