Getting there
This is a hike-to lake, not a roadside viewpoint. The usual approach starts at the Dôl Idris car park beside the A487 and follows the Minffordd Path uphill through the reserve. The lake is reached partway along the route, after a sustained climb on rough, rocky ground. Visitor reports commonly put the lake at roughly 3 kilometres from the car park, but the going is steep enough that time varies with weather, fitness and stops. The full Minffordd route to the Cadair Idris summit is 9 kilometres there and back, with 788 metres of ascent and an official duration of about six hours.
The park authority grades the route hard or strenuous and says that good fitness and navigation skills are essential. Expect steep hills, rough country and possible scrambling higher up. There is no level, accessible path to Llyn Cau, and the accessible trails and facilities around the lower Dôl Idris parkland do not continue to the lake.
