Lake Sevan covers around 1,240 square kilometres - bigger than the city of London. It was carved out by ice and water over millions of years and now sits like a giant blue bowl in the highlands of central Armenia. The water is fed by 28 rivers but only one river flows out, called the Hrazdan.
Because the lake is so high up, the water is icy cold for most of the year - even at the height of summer it is bracing. Brave swimmers run in for a few minutes, then warm up on the beaches afterwards with hot tea and grilled fish.
Sevan has its own special fish called the ishkhan, or 'prince trout'. It is found nowhere else in the world. Scientists have worked hard to keep the ishkhan from disappearing - the lake used to be much fuller but a lot of water was drained out a century ago, and the fish almost vanished. The lake is now slowly being refilled.
On a small island (now joined to the shore by a strip of land) sits one of Armenia's oldest stone buildings - the Sevanavank monastery, built more than a thousand years ago. From the top of the steps you get a view across the lake that looks like something from a fairy tale.