A fairytale cave filled with giant mineral crystals – Europe's largest – is to open to the public for the first time later this year.

The cave, or geode – a cavity of rock filled with crystals – lies 50 metres beneath an abandoned silver mine in a town in Andalusia, Spain.

First discovered by a mineralogical society from Madrid in 1999, it is hoped the cave will change the fortunes of the town of Pulpi, bringing tourists and with them jobs.

The closest this arid, coastal town of around 9,000 residents has previously come to any sort of fame was in 2007, when locals made it into the record books for tossing the world's largest salad.

Visitors to the cave will first have to walk down the mineshaft before descending newly installed staircases which will take them through the vast caverns of the mine, which closed in the 1960s.

Eventually, they will arrive at the entrance to the geode, an opening in the rock ringed by massive, white crystals.

Inside, the geode measures just 8 metres long and 2 metres high, but every inch is lined with dazzling, transparent crystals.

Geodes are formed over millions of years when a cavity inside a rock fills with liquid. "Generally, it has to get filled up completely by a saline solution, in this case liquids with calcium sulfate, which creates selenite crystals. Then it needs the right amount of time and the right temperature to form. But above all, it needs a very long time," explains geologist Francisco Fernandez Amo.

He adds: "In Europe, this is the only geode like this. Globally, there is a geode in the Naica Mine in Mexico which is even bigger but the problem with this geode is that it's at a depth of more than 200 metres, which makes opening it to the public very tricky. This is the largest geode in the world which people can visit."

The team working on the project say the official opening is set for October, but they're hoping to run preview visits in July.