Dolbadarn Castle stands on a rocky knoll between Llyn Padarn and Llyn Peris, its single round tower rising against the backdrop of Snowdon. Built by Llywelyn the Great in the early 13th century, it was the most important stronghold of the native Welsh princes of Gwynedd and the site where Llywelyn the Last held his brother Owain Goch captive for over twenty years.
The castle fell into disuse after the English conquest of Wales and was already a romantic ruin by the 18th century — Turner painted it several times, attracted by the combination of medieval masonry and mountain scenery. You can climb to the top of the surviving tower for views over both lakes and up the Llanberis Pass. Entry is free and the site is always open. From the village centre it is a ten-minute walk.