The sea looks like a desert in the town in Greece where I spent every holiday in my youth. A plain of sand that slowly, slowly gets deeper. There's one very impressive thing that happens at about 10 to 15 meters depth (maybe one mile out): suddenly the sea floor just seems to disappear. We call it Ta Mavra, wich means The Black. I tried to film this, which is actually pretty hard to get right. You probably like the colorful jellyfish better.
A clip that did work out is one where I dropped the GoPro into the depths, which looks pretty spectacular – vimeo.com/48479646