I am swimming in deep water and the clarity is now, to be honest, a little scary. Not only can I make out individual rocks on the seafloor 15 meters below, but I can see my shadow dancing down there in the deep. The afternoon has been an extended encounter with the sublime. I climbed down to this deep water along a dramatic ledge of sea-polished marble on the far side of Planitis Island. Planitis looks like an island that the Earth, for its own mysterious reasons, picked up and stuck back in the sea standing on end. Canted bluffs show off towering striations, train-sized layers of brown and white and gray rock as packed and level as wedding cake. Shoving all this stone above ground also cut into the ground massive wedges of cavern. The violent geology of this place is so visible that as I padded through the silt-fine dust in these dank and still vaults I couldn’t help but imagine one of them biting down, closing off the thin rim of blue sky above me. At the summit of this upended island, an ancient lighthouse is slowly giving way to the winds of time. Standing up there, I could see miles and miles of sea, but it was hard to look away from the spot 50 meters below, where Planitis dropped away so sudden and sheer that, again, it looked like I was suspended, dangling above the seething, coursing breakers. I could feel the plunge in my ears and my stomach and my knees. Planitis is nearly connected to Tinos by a long, not-quite isthmus of land that has been worn down by the sea in several places. The first time I scouted the passage, the wind was up and the sea was crashing through every available channel. The churning surf was a topaz-blue I have seen before only in candy. Today the channel was calm and wading across required only a little patience. In a few minutes I will climb out of this crystal water, scale up the brutal rock to level ground, and make my way back to the big island. In a few minutes. This place feels like edge of the world or, at least, the edge of life—ecstatic and terrifying and beautiful—and it’s hard to pull myself away.