UKAEA is partnering with Italian energy company Eni to build an advanced tritium fuel cycle facility at the Culham Campus in Oxfordshire. The UKAEA-Eni H3AT (pronounced ‘heat’) Tritium Loop Facility ...

The small cavern where it can be found is blocked off from its surroundings, though, and the only way you can reach it is to dive into a small pond and swim through an underwater opening.