The site of Dolwyddelan Castle has been on a major thoroughfare through Wales for millenia. Before the present castle was built by Llywelyn Fawr (Llywelyn ap Iorwerth) early in the 13th century, an older castle sat on a knoll on the valley floor below it. http://www.castlewales.com/dolw.html
Before that castle, a major Roman road through Snowdonia passed just to the east, connecting Tomen y Mur with the small fort of Bryn y Gefeilliau and the larger fort of Canovium (Caerhun). (See Roman Roads: https://sarahwoodbury.com/?p=29)
The present Dolwyddelan Castle has been heavily restored, in keeping with it’s position as the birthplace of Llywelyn Fawr, even if that even really occured a quarter of a mile southeast of the present castle.
The newer Dolwyddelan Castle represented a major stronghold for both Llywelyns throughout the 13th century. Both of them improved its defenses, luxuries, and overall structure numerous times over the course of their reign. Of Llywelyn ap Iorwerth (Wales – A History, Wynford Vaughan-Thomas, Michael Joseph Ltd. Publishing, London WC1, 1985):
“Llywelyn deliberately set out on a policy of reconstructing the whole basis of Welsh political life, and not every Welshman was happy about it. Llywelyn lived in an age which saw the emergence of the centralized feudal state. Both France and England presented the spectacle of societies elaborating their administrative machinery, putting their taxation on a new and sounder footing and systematizing their codes of justice, but Llywelyn’s principality was small and lacking resources. Hostile English observers could wax satirical about its pretensions to international status.
Gwynedd had always been the core of the power of the princes, and the expansion of Llywelyn’s territory gave him the ability to do many things beyond the power of previous Welsh rulers. We find Llywelyn ap Iorwerth (the Great) and Llywelyn ap Gruffydd (the Last) developing castle building on a considerable scale. The remains of Castell y Bere or of Ewloe, Dolbadarn and Dolwyddelan even show distinctive Welsh style. The princes gave charters to the small towns growing in their domains. They supported the abbeys and the friaries. We sense a new Wales coming into being, and, at the moment, it was basically an independent Wales.” http://www.castlewales.com/llewelyn.html
Dolweyddelan was one of the last castles that Edward I captured in the war against Llywelyn ap Gruffydd, and even then he didn’t conquer it until 1283, after Llywelyn’s death.