At the eastern end on Llyn Padarn in the Nant Peris Valley, Dolbadarn Castle was built by Llywelyn the Great, one of the Princes of Gwynedd, before the year 1230. Only the outer shell of the castle's round tower remains, but foundations of the rest of the structure give an impression of the original castle. At the foot of Snowdon, this was a position of strategic importance with the potential to prevent movement through this valley into the rest of Wales.