Antarctica hides the saltiest body of water on Earth
Don Juan Pond, a shin-deep puddle in the McMurdo Dry Valleys, is roughly 30% saltier than the Dead Sea. Its calcium-chloride brine is so concentrated it almost never freezes, staying liquid even down to -50C. Scientists study it as a stand-in for the kind of brines that might exist on Mars.
— Wikipedia contributors, Don Juan Pond — Wikipedia entry on the hypersaline Antarctic lake