High in the barren uplands of the Cambrians lies this twisting reservoir with long shale shores, many inlets and an empty road hugging its southern shores, perfect for the campervan swimmer. Rising above is the hulk of Plynlimon, the highest point in the Cambrians (752m) and source of both the Severn and the Wye. The road here feels like an epic journey in itself, even in a car, and passes several ruined mines and smaller lakes.
From west: follow lane from Ponterwyd (SY23 3JX). From the east: Turn off A487 Tal-y-bont by the White Lion and Black Lion, and follow signs for Nantymoch, past turning to SY24 5HL. At top, about 5 miles from pub, a wide L track would take you to the remotes reaches of Llyn Conach and beyond, but continue on tarmac road R (SE) at the 5 miles junction. Pass lovely Llyn Nantycagl on L after ½ mile, to reservoir after 2 miles (there are quirky fireplaces in the woods, just off the road at 52.4780, -3.8606). The main beachshore is after another 2 miles; continue up to 3 miles beyond this, turning L after the dam, to explore the little island/peninsula (52.4777, -3.8120) and the flanks of Plynlimon. At the road end (gates at Maesnant), take the R track (public byway) another mile up to the Afon Hengwm. 5 mins, 52.4706, -3.8508
from Wild Guide to Wales (Wild Things Publishing, 2018)