The masonry tower at Dolbadarn is regarded as one of the finest remaining of the Welsh castles, a memorial to Llewelyn ab Iorwerth or Llewelyn the Great. He was the undisputed Prince of Gwynedd from 1201 until his death in 1240. The strategic importance of his castles was at the heart of political power in the thirteenth century and was only finally overshadowed by Edward I.
The Castle is now open to visitors and is maintained by Cadw: Welsh Historic Monuments. Currently, there is no admission charge and free access to the Castle.

The Llys or Court was itinerant in the thirteenth century and the Welsh castles featured on these itineraries. Symbolically the castles signified to all and in particular the English Marcher Lords that the Welsh Princes were the rulers of the Welsh administrative area or "commote". Dolbadarn guarded one of the main arterial routes through the mountain ranges.

Dolbadarn was the first of the independent Welsh Castles to have a round tower. This mighty keep still stands today although only the barest remains of the Hall and other buildings can be detected. The keep was deliberately built as a mirror of earlier English equivalents especially those of the important Marcher families. For its time, the structure is sophisticated with an internal spiral staircase, which changes direction from part way up. It also has a portcullis in the entrance. Unlike other examples from that period, Dolbadarn has three storeys and the view from the top of the twin lakes and surrounding mountains is magnificent.

It is unlikely that Owain Goch would have appreciated the view. He was imprisoned here for twenty-two years in the mid 13th Century by his brother Llewelyn ap Gruffyd (Llewelyn the Last). Llewelyn had fought his nearest relatives to gain the princedom of Gwynedd and thereafter imprisoned or banished them.

The hill on which the keep stands was surrounded by a curtain wall, once ten feet high but now reduced to three feet, inside which once stood a hall, a second tower the west, a further building to the east, all set round a courtyard. Careful examination of the site will reveal these features.

Dolbadarn Castle was built on the site of an earlier structure. It is estimated that the building was erected during the latter part of Llewelyn's reign probably somewhere between 1230 and 1240. However, after Edward 1's conquest of Gwynedd in 1282-3, it was little used and finally fell into decay. It was ecstatically rediscovered by artists and travellers in the 18th and 19th Centuries and among many others was superbly portrayed by Turner.

The site has now been cleared and maintained and is still an awe-inspiring sight for visitors. It is reached from the southeast end of Llanberis just past the end of the High Street on to the main A4086 road. Almost opposite the Snowdon Mountain Railway Station turn down the lane, which leads to the Padarn Country Park and the Slate Museum. After about two or three hundred metres there is a large car park on the left. On the opposite side of the road there is a kissing-gate and a path, which leads through a wood near a stream and up hill to the castle.