13. Mariana Trench, Pacific Ocean
The Mariana Trench is the deepest known part of Earth’s oceans, plunging nearly 11,000 meters (36,000 feet) beneath the surface. This underwater abyss is a world of eternal darkness, bone-chilling cold, and crushing pressure, over 1,000 times greater than at sea level. With virtually no oxygen and only sparse life forms adapted to the extreme conditions, human survival is impossible here without highly advanced technology. Deep-sea submersibles are required even for brief visits, and even the most resilient machines are pushed to their limits.