The walk starts from Dôl Idris car park on the B4405, just off the A487 at Minffordd (LL36 9AJ, but the postcode covers a wide area, so use the Directions button). It's run by the Snowdonia National Park Authority and costs £5 for up to 4 hours or £8 for the day, so for this walk of 5 to 6 hours you'll need the daily ticket. Payment is by chip and pin or contactless only; cash isn't accepted. There are 3 Blue Badge spaces, EV charging and toilets, and no overnight camping. It can fill up at busy times, so arrive early. Check latest prices here.

Cadair Idris means "Idris's chair", but nobody is quite sure who Idris was. Most people take him to be a giant, said in legend to be skilled in poetry, astronomy and philosophy. Others link the name to Idris ap Gwyddno, a 7th-century prince of Meirionnydd who is said to have won a battle against the Irish on the mountain, and who appears in some medieval family trees of Meirionnydd as Idris Gawr, Idris the Giant. The name is old: in the 15th century the poet Lewys Glyn Cothi was already writing of travelling over Cadair Idris.

The best-known story about the mountain is that anyone who spends a night alone on its slopes will come down either mad or a poet. It seems to go back to the bards, who would sleep up here in the hope of waking with new verses. Some of the lakes nearby were also said to be bottomless.

Not every night up here was meant to be peaceful. In Welsh mythology Cadair Idris is one of the hunting grounds of Gwyn ap Nudd and his pack of huge hounds, the Cŵn Annwn. To hear them howling meant death was coming, and the pack would sweep up the soul and drive it down to the underworld. One tradition says Gwyn's chief huntsman, Iolo ap Huw, can be found every Halloween cheering the hounds on over Cader Idris, and the Brenin Llwyd is said to haunt the mountain too.

Richard Wilson was born on 1 August 1714 at Penegoes in Montgomeryshire, the son of a clergyman. He went to London in 1729 to train as a portrait painter, later turned to landscapes, spent 1750 to 1757 in Italy, and in 1768 was one of the founder members of the Royal Academy. He is now seen as one of the pioneers of British landscape painting, and alongside his Italian scenes he painted the landscapes of his native Wales.

Wilson was probably the first artist to paint Llyn Cau. He took his view from the slopes of Mynydd Moel, the hill you come down at the end of this walk, about a mile from the lake and some 500 feet above it, with the Dysynni valley to the left and Cardigan Bay in the distance. He didn't copy the scene exactly: the foreground is made up, and he made the cliff of Craig Cau behind the lake taller and more regular to give a simpler, better balanced picture. It was shown at the Royal Academy in 1774 as "A View of Caderidris Mountains in North Wales".

Before the fashion for the sublime, wild scenery like this would probably have looked raw and untidy rather than beautiful. Wilson was one of the first painters to make it work on canvas, and he went on to influence artists including Turner. In 1783 the naturalist Thomas Pennant wrote that Wilson had captured the lake so well that he would not try to describe it himself. The painting was almost certainly still Wilson's when he died; much later Sir Edward Marsh gave it to the National Gallery on VE Day, 8 May 1945, and it moved to the Tate in 1955.