If you come to this place on a day when the damp mountain mists swirl in and out of the blackened mossy crags, and when rain-soaked waterfalls drop from those mists like plumes of steam, you will experience the atmospheric menace. However, the sunshine can paint a very different picture, with golden rocks that are a playground for the modern-day climber, and small mountain birds such as the wheatear and ring ouzel flitting through the grasses.

Cwm Idwal is a perfect hanging valley, and a fine place to study geology and nature. In the last Ice Age a small glacier would have been slowly scouring its way over the cliffs at the head of the cwm before joining the huge glacier that used to fill the U-shaped valley of Nant Ffrancon. You will pass the moraines (the debris left behind by the glacier) not long after leaving the car park at Ogwen. The glaciation left a legacy in Idwal, for here in the inaccessible places free from animal grazing, rare plant species are to be found. These brought botanists from far and wide. Their favoured spots were the crags around Twll Du, otherwise known as the Devil’s Kitchen, a deep defile where the mountainside’s volcanic bedrock is divided by a column of basalt. Here was the snout of the glacier and, on the surrounding ledges and crevices, the rich soils allowed many species of arctic plants to flourish. The most famous is the rare Snowdon lily, discovered in the 17th century by Edward Llwyd. Tufted and arctic saxifrage are also here, although hard to spot, but the starry and mossy saxifrages are there for all to see, as are wood sorrel, wood anemone and oak ferns. Collectively, the foliage seems to flow down the rocks and you can see why it’s called the Hanging Gardens. Climbing above the rocks, the path attains a wild and windswept hollow of moor grass and rushes. Llyn y Cwn (‘dog lake’) is a shallow pool tucked beneath the loose boulder and shale slopes of Glyder Fawr. In summer bogbean rings the pool’s outer edges with its pale pink blooms. This is a fine, lofty place to dwell and admire the mountain views before going back down to the cauldron of Idwal.

The Cwm Idwal nature trail starts to the left of the Snack Bar at Ogwen, and climbs up the hillside to pass some impressive cascades. Ignore a narrower path left, just before the main path swings right.

Arriving at the foot of Llyn Idwal, turn left along its eastern shores. The clear footpath climbs into the dark shadows of Cwm Idwal.

Now you leave the nature trail, which forks right to complete a circuit around the lake. Instead ascend beneath the rock climbing grounds of the Idwal Slabs and across the stream of Nant Ifan, beyond which the footpath zigzags up rough boulder ground to the foot of Twll Du – the Devil’s Kitchen. If the the forecast is fine, climb to Llyn y Cwn at the top, if not, go to Point 6.

To ascend Twll Du climb the engineered path as it angles left up the rock face, which will now be on your right-hand side, above an extensive area of scree and boulder. At the top you come to a relatively gentle grassy hollow between the rising summits of Y Garn, to the right, and Glyder Fawr, to the left.

Just beyond the first grassy mounds you come across the small tarn of Llyn y Cwn – the Dog Lake – which makes a great picnic spot. Now retrace your steps carefully to the bottom of Twll Du

Among some huge boulders, the path forks and the left branch heads down to run above the western shore of Llyn Idwal, then rounds its northern end to meet the outward route at Point 2. The fork is easily missed; if you do this, continue down below the Idwal Slabs and turn left on the nature trail to round the lake. Now follow the route of your outward journey back to the car park at Ogwen.