This is a natural salt cave - they're really common in America, Eastern Europe and Russia.
For centuries they've been used to help with problems to do with our lungs - allergies like hayfever and asthma - and now one's been recreated in the UK.
The UK's first salt cellar has just opened its doors in London, so Gavin went along to check it out...
The special salt cave has its own climate, and the levels of salt in the air are carefully controlled.
Georgiana and her brother Toby have been having sessions at the salt cave and say their coughs and sneezes have got much better.
The idea is the kids breathe tiny particles of salt into their lungs while they play, which helps dissolve the gunk in their airways that makes them wheezy.
They lay out plenty of things to do in the salt cave while the children are having their sessions. There's book and toys, and always the salt to play with - like a giant sand pit!