The Mariana Trench or Marianas Trench has the deepest part of the Earth's ocean, the Challenger Deep. The bottom there is 10,924 meters (35,840 feet) below sea level. Mount Everest could be completely submerged in that depth, and still its top would be one mile underneath the surface. It was named after the British survey ship Challenger II, which discovered this location back in 1951.
Photos and link: wikipedia