More is known about the terrain of Mars than about what lies hidden beneath the Earth’s surface. Krubera Cave in the republic of Georgia is currently the deepest known cave, at 7,208 feet.

One such drop is known as Fantastic Pit within Ellison’s Cave. It is the deepest freefall pit in America, plunging down vertically for 179 meters (586 feet). Within the same system is Incredible ...

From a protected cove on Long Island, Dean’s Blue Hole—Earth’s deepest known underwater cave—plunges more than 600 feet into darkness. The entry to South Passage is decorated by ...

The Burj Khalifa would go 2,722 feet below the surface. The deepest known point in a cave is in Krubera Cave in Georgia. Switzerland's Gotthard Base Tunnel is the deepest railway tunnel.

Now, digital analysis of rock surfaces reveals how other ghosts of the deep past—this time from ... are some of the largest known cave images found in North America and may represent spirits ...