Undersea mine in the UK

The BBC has an article (with its usual unbloggable video) about a mine that goes down and out:

The Boulby mine in northern England is where much of Britain’s potash, used in fertilizer, is collected. But to do so they have to tunnel kilometers under the sea.
The mine is located more than 1,400 meters, nearly a mile, underground. Its tunnels are humid and reach temperatures of up to 40°C. It’s from here that Britain gets much of its potash, the potassium-rich salt used in fertilizer.
Boulby is the second-deepest mine in Europe, but it’s not the only thing that sets it apart; its tunnels extend several kilometers out to sea. Here, miners work to get the ore needed to help Britain grow its food, deep below and far from shore.

Rico says it's yet another place he's glad he never had to work...