In 2000, miners in Naica, Mexico, broke into a cavern lined with giant gypsum crystals, some about 12 m long and weighing several tonnes. They grew over hundreds of thousands of years in hot, mineral-rich water. But the air there tops 50 °C with nearly 100% humidity: without a cooled suit, a person can only last a few minutes.
On 27 August 1883, the eruption of the Indonesian volcano Krakatoa was heard as far away as Rodrigues Island, nearly 4,800 km away. Its pressure wave was picked up by barometers worldwide and circled the globe several times. The tsunamis that followed killed more than 36,000 people.
The deepest known point in the ocean, Challenger Deep, lies roughly 10,900 m below the Pacific surface. Drop Everest in and its summit would still sit about 2 km underwater. Down there, the pressure is more than 1,000 times what you feel at sea level, roughly a tonne pressing on every square centimetre.