Say hello to the Kola Superdeep Borehole, pictured above, the deepest hole on Earth.

What, it doesn’t look like a hole to you? Listen, that cap is there to save your ankle, because while Smithsonian says this hole has only a 9 inch diameter at its base, it goes down 7.5 miles into the Earth, or 40,230 feet. That sounds deep, and it is deep — deep enough to uncover Precambrian, microscopic plankton fossils, which was a win for science! — it still descends only halfway to the mantle. Dang. As with so many scientific quests in the 20th century, the Kola Superdeep Borehole was a result of (sigh) Cold War tensions, as Mental Floss explains. The U.S.A. dropped their own “let’s reach the mantle” dig, labeled Project Mohole, in 1958, leading to the Soviet Union to pick up the ball four years later. Following this, the Russians plugged away at their hole for over twenty years … until a flood of demonic monsters climbed out of the pit and ate them. Just kidding, about the last part. The real problem was the fact that in 1992, the drillers hit crazy hot temperatures of 356 degrees Fahrenheit, which totally messed up their equipment. Bummer. Nonetheless, the Kola Superdeep Borehole remains one of the great scientific achievements in Russian history, according to Atlas Obscura, and you can still visit it today.

Here’s another weird twist: while the Kola Superdeep Borehole certainly is the deepest man-made hole on Earth, it’s not the longest. That honor goes to an oil well drilled in 2008, according to Gulf Oil and Gas, in Qatar. The disparity comes down to Earth’s general unevenness. Basically, while the Qatar hole is technically over 100 feet longer, the Russian hole goes far deeper underground.