If you are traveling to the outskirts of a city called Pulpí in Spain, you will find an abandoned silver mine. Descend about 50 meters (164 feet) into it, and you will enter a strange, shining room, quite unlike anywhere else on Earth.
This incredible natural space is the Geode of Pulpí, the closest thing in real life to the Superman Fortress of Solitude: an incredible egg-shaped cave where jagged pieces of shiny, transparent crystalline jute from the walls like teeth in the mouth of a dragon.
In terms of geodesy, Pulpí is a giant – in fact one of the largest known surveyors in the world.
With regard to the cavernous chambers, although it is actually small, but large enough to accommodate many people inside it at once, which is not something you can say about most geodesic cavities.
Just be careful and trust with anyone you enter inside: the hollow space in the heart of geodesy there are only about 11 meters of cube, and with all those sharp crystalline deposits protruding from the walls, there is definitely no room for pressure.  It is known that there are other grand crystal caves ound the world – most notably the famous Naica crystals in Mexico – but how do these remarkable entities emerge?
In the case of Pulpí – which was discovered only 20 years ago – the geochemical origin of the geode crystals remains largely unknown, with a seemingly even more mysterious look than its cavernous counterparts.
"Detecting their formation was a very difficult task because, unlike in the case of Naica, where the hydrothermal system is still active, the great geodetic Pulpí is a fossilized environment," explains geologist and crystallography expert Juan Manuel. Garcia-Ruiz from the University of Granada, senior author of a new survey of geodesy.
 In a new study, Garcia-Ruiz and his team seek to reconstruct the geological history of the Pulpí Geodata by analyzing samples of Mineral and geochemical environments, as well as mapping in detail of the geological structures of the mine surrounding the crystalline chamber. provided by the dissolution of anhydrite (anhydrous form of calcium sulfate).
This process, occurring at a temperature of about 20 ° C (68 ° F), is enhanced by a thermodynamic phenomenon called Ostwald maturation (or maturation). (Ostwald), together with temperature k the slopes to which the geodesy was exposed at its relatively shallow. depth in the mine.
One remaining mystery, however, is exactly when all this crystal formation took place.
Due to the extreme purity of the crystals inside the surveyor – which are so perfectly clear that you can see them straight through them – it is difficult to date the pieces, although the team has several ideas.
"They have grown safely since the drying of the Mediterranean, 5.6 million years ago," says Garcia-Ruiz.
'They are probably less than 2 million years old, but older than 60,000 years, because this is the carbonate crust age that covers one of the largest gypsum [crystals]. "
This is a rather long time difference, which increases the possibility that other foot researchers may again try to narrow the gap.
Until you do, you can check the Geode of Pulpí yourself, with the Spanish authorities opening a visitor site earlier this year – giving everyone a chance now to enter this very strange and special sanctuary of sorts.
"Bending your body between huge crystals is an incredible feeling," explorer Javier Garcia-Guinea discovered the formation , he explained to the BBC in 2000.  "When I was little, I dreamed of flying, but never going to geodesy internally covered with transparent crystals."
The findings were reported in Geology .