If only it were in Indiana....

And, Legolas, when the torches are kindled and men walk on the sandy floors under the echoing domes, ah! then, Legolas, gems and crystals and veins of precious ore glint in the polished walls; and the light glows through folded marbles, shell-like, translucent as the living hands of Queen Galadriel. There are columns of white and saffron and dawn-rose, Legolas, fluted and twisted into dreamlike forms; they spring up from many-coloured floors to meet the glistening pendants of the roof: wings, ropes, curtains fine as frozen clouds; spears, banners, pinnacles of suspended palaces! Still lakes mirror them: a glimmering world looks up from dark pools covered with clear glass; cities. such as the mind of Durin could scarce have imagined in his sleep, stretch on through avenues and pillared courts, on into the dark recesses where no light can come. And plink! a silver drop falls, and the round wrinkles in the glass make all the towers bend and waver like weeds and corals in a grotto of the sea. Then evening comes: they fade and twinkle out; the torches pass on into another chamber and another dream. There is chamber after chamber, Legolas; hall opening out of hall, dome after dome, stair beyond stair; and still the winding paths lead on into the mountains' heart. Caves! The Caverns of Helm's Deep! Happy was the chance that drove me there! It makes me weep to leave them.

Apparently Gimli's been to Mexico:

A sort of south-of-the-border Fortress of Solitude, Mexico's Cueva de los Cristales (Cave of Crystals) contains some of the world's largest known natural crystals—translucent beams of gypsum as long as 36 feet (11 meters).

...

Modern-day mining operations exposed the natural wonder by pumping water out of the 30-by-90-foot (10-by-30-meter) cave, which was found in 2000 near the town of Delicias. Now García-Ruiz is advising the mining company to preserve the caves.

"There is no other place on the planet," García-Ruiz said, "where the mineral world reveals itself in such beauty."

But there is an interesting question to be considered:

Thanks to the 13,200 gallons (55,000 liters) of water pumped out of the mine every minute, the acres surrounding the mountain have been rendered ready for farming—a rarity in Naica mountain's Chihuahuan Desert setting

This same epic pumping operation makes it possible for humans to study the Cave of Crystals. If the pumping is stopped, the caves will again be submerged, and the crystals will start growing again.

So what happens if—or when—the mine is closed?

"Should we continue to pump water to keep the cave available so future generations may admire the crystals?" geologist Juan Manuel García-Ruiz said. "Or should we stop pumping and return the scenario to the natural origin, allowing the crystals to regrow?"

Pictures, all taken from National Geographic's website: