The Ocean Floor
You might think that the ocean floor is like a flat desert underwater but it is not it is with hills, trenches, planes, valleys, canyons, and volcano's.
People never new how to get down to the ocean so they thought that there was sea monsters down there.
In world war 1 they mapped the ocean floor then they used submarines
All kinds of animals live on the ocean floor like a school of fish, plankton, dolphins, starfish, lobsters, and clams.