Lake Nemrut is a cold, crescent-shaped lake sitting inside a collapsed volcano, with a bath-warm second lake a short walk from its shore. The caldera around them is 8.3 by 7 kilometres, the largest in Turkey. From the rim the whole bowl opens at once: the dark blue of the main lake, the jade green of Ilıgöl beside it, and black tongues of lava between the two. The big lake drops 176 metres deep at an altitude of 2,247 metres. Ilıgöl is shallow and fed by hot springs rising along a fault in the caldera floor, and people have long sat in it for their aching joints. This volcano made Lake Van. Roughly 250,000 years ago Nemrut pushed out a lava flow more than 60 kilometres long that blocked the Murat valley, and the water backing up behind it became the largest lake in Turkey.
Woods of birch and trembling aspen run down to the water, a relict of colder ages and unusual at this height. For about ten days each October they turn gold, often under the season's first snow on the rim. Steam still seeps from cracks in the ground; the mountain is dormant, not dead, and last erupted in 1692. Snow closes the access road for much of the year, so the basin is normally open from late spring into late October. One rule now outweighs the view. Visitors hand-fed the caldera's brown bears until the animals lost their fear and began attacking people, and the site was shut through the winter of 2024. It reopened in May 2025: keep your distance, feed nothing, light no fire. Anglers work the shore of the cold lake, and the meadow between the two waters flowers across the reed beds in early summer.