In 1488 Maredudd ab Ieuan, a member of a family from neighbouring Eifionydd, purchased the lease and repaired the structure, but it was ruinous by the mid-nineteenth century.

Between 1848 and 1850 the keep was restored and reconstructed by Peter Drummond-Burrell, 22nd Baron Willoughby de Eresby, and in 1930 the castle was placed in state care; it is currently managed by Cadw, the Welsh Government's historic environment service, and open to the public.

The castle is built on a small knoll and consists of a keep on the east side and a tower on the west, linked by walls to form a roughly circular enclosure.

Tomen Castell may have been built by Iorwerth Drwyndwn, the father of Llywelyn and eldest son of Owain Gwynedd, to assert his authority in the period of unrest after the death of the latter in 1170.

[a][7] The castle was built at Ffriddgelli, one of the ten hafodydd, or summer cattle grazing pastures, which belonged to the princes of Gwynedd in the Lledr valley.

[8] The rectangular keep is typical of those constructed by the Welsh princes in the thirteenth century, and bears a resemblance to the contemporary towers built by Llywelyn at Castell y Bere and Criccieth.

[11] It is uncertain when the west tower at Dolwyddelan was constructed, but it was certainly built after the curtain wall and the surviving dressed stone suggests a late thirteenth or early fourteenth century date.

[c] Alternatively, it may have been erected after the capture of the castle by Edward I's forces on 18 January 1283, as a surviving account from the same year mentions the construction of a camera (lodging) at Dolwyddelan.

[16] English troops maintained a military presence at the castle until at least 1290, when Gruffudd ap Tudur, the Welsh constable appointed in 1284, was still in office.

The country surrounding Dolwyddelan was unruly, and although Maredudd built a new house, Tai Penamnen, nearby he may have valued the castle as a secure residence.

[20] It is possible that he heightened the keep, but Richard Avent considers it more probable that this work was undertaken by Edward I and that Maredudd instead preferred the spacious chambers in the west tower.

It was engraved by Samuel and Nathaniel Buck in 1742 and painted in 1788 by Moses Griffith for inclusion in Thomas Pennant's A Tour in Wales, which includes a description and history of the castle.

[25] These accounts are valuable as they record the castle before it was partially restored and reconstructed by Lord Willoughby de Eresby, a distant descendant of Maredudd ab Ieuan, between 1848 and 1850.

[29] Dolwyddelan Castle forms a roughly circular enclosure around the knoll it occupies, and is constructed of local grit and slate rubble.