Ocean descent is about weight, slowness, tonnes of sea water bearing down, and the discomfiting realisation that humans are alien to most of our own planet.
I just read a pretty amazing article covering a brief history of deep ocean exploration. The deep ocean was one of my obsessions when I was little, just like dinosaurs and Star Wars (not uncommon, I think). I guess I moved on, but the author's descriptions of the deep sea definitely rekindled my interest. I bet the library has a copy of 20,000 Leagues Under the Sea.