Somewhat overshadowed by the giant Dinorwig Quarry which towers above the village of Llanberis, there are also major quarry remains on the low mountain of Cefn Du. The Glyn Rhonwy Quarry is dug into the hill from lake level to the very top of the mountain. Massive tectonic forces, during the ancient collisions 400 million years ago that built the mountains of Snowdonia, have shoved the Glyn Rhonwy Quarry one kilometre further north-west from the Dinorwig Quarry. Nowadays the Glyn Rhonwy is largely hidden from view by trees, unlike the conspicuous Dinorwig Quarry but a wlak through the old quarries reveals their vast effect on the landscape. Cefn Du was also the site of the antenna used by Guigilemo Marconi a century ago to transmit the first transatlantic wireless transmissions and some remains of the antenna can still be found in the summit area. The summit area also offers stupendous views of the mountains of Snowdonia and towards Anglesey. Thus, this walk combines fine walking, great views and a wealth of industrial archaeology.
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