There’s a tiny island in the Southern Ocean where beaches are packed with penguins, elephant seals lounge in the surf, and the ground beneath your feet once sat miles below the seafloor. And yet somehow, that’s not even the strangest part.

Welcome to Macquarie Island, a 21-mile-long sliver of Australian territory approximately 930 miles southeast of Tasmania, halfway to Antarctica.

In an insightful and fascinating new Astrum Earth video , narrator James Stewart calls it “a tiny island that shouldn’t exist.” Check it out below.

The reason? You can walk on rocks from Earth’s mantle.

“You don’t need to drill to find the mantle,” Stewart explains, because those rocks are already at your feet.

According to UNESCO , Macquarie is the only place where mantle rocks are being actively exposed above sea level. Typically buried roughly four miles beneath the ocean floor, these ancient formations were pushed upward as the Indo-Australian and Pacific tectonic plates squeezed together.

It’s not a volcano, either.…