Göygöl is a lake in the Lesser Caucasus of western Azerbaijan, near Ganja, and it was made in a single night. In 1139 an earthquake tore the flank off Mount Kapaz and dropped it into the valley below. The river had nowhere to go after that. What holds the water in is nothing but the wreckage. Dams like it are not supposed to last: the lake rises behind loose rock, spills over the top and saws the barrier away, usually within months. This one has held for nearly nine hundred years, with six smaller lakes from the same collapse still sitting higher up. The path in comes through beech forest and breaks out of the trees with the whole lake below you, a long blue sheet closed off by wooded ridges. Kapaz stands 3,066 metres over the far end, and the bare face is where the mountain let go. Cloud works across the summit all day, so it shows and hides while you watch; when it clears and the water is still, the whole mountain lies on the surface. Nobody swims here; you look at the lake from the shore path.
The walking goes up. Above the forest belt the beeches give out and the slope opens into rough grazed grassland. Only from there do you see how completely the park is buried in trees: ridge after ridge, with the lake a small blue interruption somewhere below. A forest trail carries on to Maralgöl, a smaller lake from the same landslide, set higher in the mountains and left alone by most day visitors. Through October the beech and hornbeam around the shore turn gold and rust, and the still water repeats them upside down. On the road up stands a town founded in 1819 by Swabian settlers, who called it Helenendorf and made wine here for a century before they were deported to Central Asia in 1941. In 2008 it was renamed after the lake. The trout in the water are river fish. The rockfall shut them in above the new wall in 1139, and they have been breeding among themselves ever since.