The Hranice Abyss in the Czech Republic is the deepest known freshwater cave in the world. Reaching a depth of over 1,500 feet, it is so deep that the world’s tallest building, the Burj Khalifa, could fit inside it. Recent research has revealed the surprising formation of the abyss, challenging previous scientific beliefs. The cave was carved from the top down by water over millions of years, and its connection to a nearby fossil sinkhole sheds light on its geological history.