There's a lake on Earth and no one has ever even seen it.

It's the 16th largest on our planet, about 160 miles long, 30 miles wide, 3,000 feet deep and trapped under two and a half miles of ice in East Antarctica.

Lake Vostok is the largest known subglacial lake in Antarctica, and it has been hidden beneath the ice for at least 15 million years.

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It's an ancient environment and one of the most isolated places on Earth that remains very much a mystery to us today.

(MORE: A record-breaking T. rex, an Antarctic fossil, and the climate clues in dinosaur bones)

Since Vostok's discovery, more than 350 smaller lakes have been located in Antarctica.

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"Lake Vostok is absolutely devoid of interference,” Robin Bell, the Columbia scientist who helped map it, said. “It doesn't know anything of human beings, fossil fuels or plastics."

The geological science at play

You might be wondering, if this lake is trapped under ice in Antarctica, why isn't it frozen?

The answer lies in the question: it isn't frozen because it is trapped under ice.

The surface above the lake hits a chilling minus 76 degrees Fahrenheit. But the miles of ice above it work like a blanket, trapping heat leaking up from inside the Earth.

That keeps the water at about 26.6 degrees Fahrenheit — still very cold, but kept in a liquid state because of the geothermal heat that prevents it from freezing.

(MORE: Antarctica breaks decade-long cold record with Earth's lowest temperature)

The water is actually gradually replaced over thousands of years too. It is slowly replenished by meltwater from the ice above.

Although the lake is ancient, the waters are comparatively young, since they depend on the age of the ice that melts to form it, which is around 700,000 years old.

Space lake, grounds for astrobiological studies

There's something alive in Lake Vostok.

When researchers took some frozen lake water, they found microbes inside of it — enough to suggest a real, complex microbial ecosystem down there.

They found both psychrophiles, organisms that live in extreme cold, as well as thermophiles, which live in extreme heat. The cold makes sense, but the heat is a bit surprising and supports the theory that hydrothermal vents, which can be found in hot springs, are hiding at the deepest parts of the floor of the lake.

(MORE: We discovered an atmosphere on an Earth-like planet in a star's habitable zone)

But all of this opens up an entirely new line of questioning: if we can find this on Earth, could these mysteries also be hiding on other planets?

Some moons in the solar system, such as Jupiter's moon Europa and Saturn's moon Enceladus, also have oceans of liquid water beneath their thick, icy shells.

These similarities make Lake Vostok almost like a mini version of these icy moons, and studying it further could show us a glimpse of what we could expect to find there.

NASA is paying close attention, calling Antarctica's subglacial lakes "one of Earth's final frontiers" and "a major research focus of astrobiology."

Content writer Ada Wood enjoys exploring the stories that science and climate teach us about our natural world and how it influences the way we live in it.