The Dead Sea is a salt lake whose surface lies about 430 m below sea level, the lowest point on dry land. Its water is nearly ten times saltier than the ocean, so dense that you float without effort. But it evaporates faster than it is replenished: its level is dropping by about a metre a year.
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.