Sørvágsvatn, the Lake Above the Ocean — Vágar, Faroe Islands

This is the most photographed optical illusion in the North Atlantic. From the clifftop at Trælanípan — the Slave Cliff — the lake behind appears to hover hundreds of metres above the sea, as though someone had propped a sheet of fresh water up on the edge of the island. It does sit above the ocean, but by about thirty-two metres, not the dizzying height the picture suggests. The trick is entirely a matter of where you stand: the cliffs on either side of the lake's outlet rise much higher than the water, so a low vantage point near the edge lines them up in a way that flattens the distance and lifts the lake. What keeps the lake from draining altogether is that ring of higher rock, broken in just one place by the waterfall Bøsdalafossur, which tips the overflow straight into the Atlantic.

The lake has three names and the islanders do not fully agree on any of them. People in Sørvágur, to the west, call it Sørvágsvatn — the lake by Sørvágur. People in Miðvágur and Sandavágur, to the east, prefer Leitisvatn, after the land on their side. Most locals sidestep the argument entirely and simply say Vatnið, 'the lake', because on Vágar there is really only one worth mentioning: at 3.4 square kilometres it is the largest in the Faroe Islands, more than three times the size of Fjallavatn on the same island. Its quiet stretches hold brown trout, and boat excursions have run on it since a local initiative started them in the summer of 2005. During the Second World War the British army built an airfield just west of the water — now Vágar Airport — along with a seaplane station, and the first aircraft to touch down on the lake itself was a Catalina flying boat in 1941.

As a puzzle this one rewards patience, because almost half the frame is rock in slightly different browns. Start with the geometry that only appears once: the vertical face of Trælanípan dropping into the water, the narrow gap of shadow behind it, and the white collar of surf where the Atlantic breaks against the base. The snow line across the top of the plateau is your second anchor — it gives a hard light-dark boundary running right across the image. Leave the open sea for late; it is a deep, even teal with very little variation, and it is best sorted by how much white foam a piece carries rather than by shape. The pale sky and the frozen lake surface shade into one another near the horizon and are the honest difficulty here, so save them for the end.