The Challenger Deep in the Mariana Trench is the deepest known point in Earth's oceans with a measured depth of approximately 36,000 feet below sea level.
Mariana Trench is a very deep, crescent-shaped trench beneath the surface of the Pacific Ocean to the southeast of Japan.
The Challenger Deep is named after a British Royal Navy ship called the HMS Challenger. The Challenger was the first ship to measure the depths of what is now known as the Challenger Deep."
Just to give you an idea about the depth of the Mariana Trench is, if Mt. Everest were placed in the deepest part, there would still be over a mile of water above its peak.