Dolmelynllyn Estate is an area of farmland, woodland and parkland near the village of Ganllwyd in southern Gwynedd, Wales. It is owned by the National Trust. The estate was formerly owned by William Madocks, the architect of Porthmadog. Features of the estate include ancient woodland, temperate rainforest, rare lichens and mosses, as well as archaeological features from prehistoric cists to nineteenth-century gold mines. The estate also has 46 bee boles on it, which is the highest concentration in the United Kingdom.

William Alexander Madocks was a British politician and landowner who served as Member of Parliament (MP) for the borough of Boston in Lincolnshire from 1802 to 1820, and then for Chippenham in Wiltshire from 1820 to 1826. He is best known, however, for his activities as an agricultural improver in Gwynedd, especially around the towns of Porthmadog and Tremadog which he founded and which are named after him.