The Cave of the Crystals, discovered in 2000 in northern Mexico, is an underground cavern (formerly and now again filled with water) with enormous gypsum crystals in it; it is deep enough, and humid enough, that when scientists went down to study it they required refrigeration suits to survive the high temperature, and to keep the extremely wet, warm air from filling their lungs with condensation.
Obviously it’s not a surprise that such a thing can exist, but it still feels like a startling discovery to me. That it does means there may be more like it; or other similarly spectacular underground formations in Earth’s crust (or maybe even mantle?) that we’re totally unaware of. It’s a cool reminder of just how little of the world around us, or the further universe, is directly accessible to observation and how many spectacular or interesting things remain to be discovered.
How could you not post photos? “giant” doesn’t convey what these caves are.
Brinens and Things 