And sometimes the surface of the water isn't the surface either. Fuck going in caves. "For everyone asking about the surface not being the surface — I am referring to a phenomenon known as a halocline, which occurs when waters of different densities mix and separate into different layers that form the illusion of the water’s surface from below. Potholing, as it turned out in this instance, meant going into *very narrow* caves. Specifically, crawling through squeeze after squeeze after squeeze so tight you could scarcely breathe, in air that did not move, encased by millennia of rock that absorbed all sound.