Answer:
Challenger Deep is a feature of the Pacific Ocean.
How difficult is it to get to Challenger Deep?
With a depth of 10,902 to 10,929 m by direct measurement from deep-diving submersibles, remotely controlled vehicles, and benthic landers and slightly more by sonar bathymetry, the Challenger Deep is the deepest known point in the Earth's seafloor hydrosphere. The H.M.S. Challenger, a Royal Navy vessel that traveled around the world in the 19th century to investigate the waters, gave rise to the name Challenger Deep. On March 23, 1875, the Challenger crew performed an action they would go on to repeat more than 500 times over the course of their three-and-a-half-year expedition: they dropped a hemp rope weighed down with iron sinkers into the water to gauge the depth of the ocean floor. This was done 140 miles southwest of Guam, at the far western edge of the Pacific Ocean. 4,475 fathoms are the result (8,184 m). The sounding wasn't a record, but it was the first one conducted near the Mariana Trench, which is now known to be the deepest place on Earth. Even if it is so deep that it could easily contain Mount Everest in its entirety, we won't be able to view the mountain's summit above the water. Although the phrase "Challenger Deep" is frequently used to refer to the deepest point on Earth, neither a sounding nor a specific area of the ocean bottom can be considered Challenger Deep. This is "deep." I will return to this shortly. Eight tons per square inch of crushing water pressure, or around 1,000 times the average air pressure at sea level, is present at the bottom of the trench. As depth deepens, pressure rises. It has been more than 50 years since the first and only time that humans entered the Challenger Deep. Imagine yourself taking on such intense pressure that, should your submersible vehicle malfunction, your body would be squeezed before you would drown. You won't find a single vertebra there as a result of this. For us as humans, it's a very other universe. There is also total darkness, which will scare the living daylights out of you. Therefore, it is true to say that we have learned considerably more about space than we have about our seas.
Cheers,
ROR