Beneath Vostok Station in Antarctica lies a lake of liquid water about 250 km long, capped by nearly 4 km of ice. It stays liquid thanks to geothermal heat and to pressure that lowers the melting point of ice. Cut off from the atmosphere for a very long time, possibly millions of years, it is one of hundreds of subglacial lakes mapped under the continent.
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.