Dolbadarn Castle was one of three castles begun by Llywelyn ap Iorwerth in the early twelfth century to defend the passes into Snowdonia, together with Dolwyddelan Castle and Castell y Bere. It sits at the tip of Llyn Padarn, which then, as now, was on a main route through Wales, and thus allowed the garrison to control movement through the north. The castle consists of the finest surviving example of a Welsh round tower with adjoining stone walls. There are two further 'towers', but these were never of a great height. By contemporary standards it was a sophisticated example of military architecture, with a portcullis at the entrance and complex stairway in which the spiral reverses direction at the halfway point.
It is probable that the tower of Dolbadarn was the site of Owain ap Gruffud's long imprisonment, from 1255 to 1277. The castle fell into English hands after the defeat of Llywelyn ap Gruffudd in 1282 and was soon supplanted by Edward I's new fortification at Caernarfon, and so was partially dismantled and abandoned. Little is recorded concerning the castle after the early fourteenth century, though there is a suggestion that Owain Glyndwr used the castle to imprison captives circa 1400.