The hike starts at the Ogwen pay & display car park by the visitor centre (LL57 3LZ, but the postcode doesn't take you straight there, so use the map directions above). It's small and fills up quickly, so arrive early or be ready to wait (I've waited up to 20 minutes). It costs £3 for 4 hours or £6 for the day, card or contactless only, and tickets run out at midnight; check the latest prices here. The mobile signal is poor, so download the route before you arrive, and if it's full there are more options below. For public transport, click "Directions" and choose public transport (the little train icon).

According to legend, the lake’s name is a lasting tribute to Idwal, the son of the 12th-century prince Owain Gwynedd, known not for martial prowess but for his intellect and grace. In an age where valour in battle was the hallmark of nobility, Idwal’s scholarly nature made him an anomaly. To shield him from the perils of war, his father entrusted him to the care of his uncle, Nefydd, a decision that would lead to heartbreak. Nefydd harboured a corrosive envy, his own son Rhun lacking the brilliance that came so effortlessly to Idwal.

One fateful day saw Nefydd and the boys near the serene lake we see today, a setting that belied the darkness that would unfold. In a moment marred by malice, Nefydd betrayed his charge, pushing Idwal into the icy embrace of the waters below. As Idwal succumbed to the depths, Nefydd’s laughter echoed, a chilling testament to his vile act.

The ripple of this tragedy extended far, with Prince Owain Gwynedd’s grief profound and unyielding. In a land where family ties were sacred, such betrayal was unforgivable. Nefydd was cast out, condemned to live with the weight of his deeds. In remembrance of his son, whose potential would remain unfulfilled, Owain named the lake ‘Idwal,’ a memorial etched in the annals of history.

Cwm Idwal's story stretches back over 450 million years. During the Ordovician period, Wales lay beneath the Iapetus Ocean. Volcanic eruptions spewed ash and lava, accumulating on the seabed alongside sediments. Then, tectonic plate collisions squeezed and folded these layers, eventually thrusting them upwards to form the mountains we see today. Evidence of this dramatic history is visible in the fossils and the varied rock types, like volcanic ash deposits and pillow lavas formed underwater.

The Cwm, also known as a corrie or cirque, owes its formation to the relentless forces of glacial erosion over thousands of years. Its steep cliffs and U-shaped troughs stand as enduring monuments to the power of natural forces, reminding us of the vast timescales and immense energies involved in shaping Earth's landscapes. For more information on Cwm formation see the above video, courtesy of Geography Simplified.

Upon Charles Darwin's first visit in 1831, with the geologist Adam Sedgwick, the pair searched the rocks for fossils from the seabed of the old Iapetus Ocean, but neither of them noticed the signs of ice all around them.

When Darwin returned in 1842 he saw it straight away: the scratched rocks, perched boulders and moraines had all been left by glaciers. He wrote that a house burnt down by fire did not tell its story more plainly than this valley.