In 1774, the bishop of Derry (fourth earl of Bristol, Frederick Augustus Hervey), built a palatial home amid a 160-hectare demesne. The house burnt down in 1851, was rebuilt in 1876, and abandoned after WWII. The ruins now stand forlornly on a clifftop, with beautiful landscaped gardens below.
The colonnaded, dome-capped Mussenden Temple, built by the bishop for his library (some say his mistress), is a Game of Thrones icon.
Enter via the Lion's Gate or Bishop's Gate.
Nearby is whitewashed, 17th-century Hezlett House (open 11am to 5pm from June to September, weekends only April to June), one of Ireland's oldest thatched cottages, which belonged to the same family of dairy farmers for over 300 years. The rooms are set up as they would have looked in Victorian times. It's 2km southeast of Downhill Demesne on the Mussenden Rd.