Or, more soberly: the writer Si Spurrier’s column for this week is very good:
I was diving alone the other day in a quiet lagoon beneath a series of jagged cliffs. Perfect conditions for Creepiness abounded: the visibility wasn’t great, the seafloor was a mangled confusion of sharp ridges (urchins, anemones and polyps) and deep crevices with thick snakelike weeds coating the slopes. At any time one was either dodging Spiky Bits just beneath the surface, or hanging above inky canyons with no visible floors; just an off-putting nebulous impression of distant movement.
I crossed one of the ridges and found a deep recess beneath the lip of the cliff. Not quite a sea-cave, but a natural dead-spot where the waves flattened out and the topography of the ocean-floor rose up: a sort of natural womb of jumbled boulders and wispy seagrass; all of it toned a perfect emerald green. Still pretty deep — ten, fifteen metres — but suddenly crystal clear. And in the middle of it, on the bottom, a chair…
(but he totally poos himself later on in the story)