Dundarg Castle is a ruined castle about 2 kilometres (1.2 mi) north-northeast of New Aberdour, Aberdeenshire, Scotland, built within the ramparts of an earlier Iron Age promontory fort. It was described by W. Douglas Simpson as one of the nine castles of the Knuckle, referring to the rocky headland of North-East Aberdeenshire, and by Charles McKean as "Scotland's answer to Tintagel". It became a small Celtic monastery for a period.

The site consists of a triangle of gently sloping ground flanked by steep slopes on all sides, linked to a flat-topped elongated promontory extending to the north-east, surrounded by 20 metres (66 ft) high sandstone cliffs. Its name comes from the Gaelic dun dearg, meaning red fort or castle, referring to the colour of the sandstone.

The 10th-century Book of Deer records the existence of a cathair or fortified place at Aberdour.

It was built in the 13th century by the Comyn family, but was dismantled, probably by Robert the Bruce, in 1308. It was rebuilt in 1334 by Henry de Beaumont, but slighted almost immediately, after a famous siege by Sir Andrew Moray. Many medieval objects providing evidence of this double destruction were found in excavations in 1911-12 and 1950-51, led by W. Douglas Simpson.

The only substantial part of the castle remaining is the inner gatehouse, which survives to a height of about 18 feet (5.5 m). The upper part was rebuilt in the middle of the 16th century, probably following the Coastal Defence Commission of 1550, and there is some evidence that it was provided with gunloops at that time. The site was finally abandoned in the mid-17th century. A house was built on part of the site in 1938, reputedly by and for Wing Commander David Vaughan Carnegie, using stone from the former Aberdour Free Church.

The castle and promontory fort are protected as a scheduled monument, while the modern house is a category B listed building.

• Beveridge, W. (1912). "Excavations at Dundargue Castle" (PDF). Proceedings of the Society of Antiquaries of Scotland. 48: 184–91. Retrieved 15 October 2008.
• Fojut, N.; Love, P. (1983). "The defences of Dundarg Castle, Aberdeenshire" (PDF). Proceedings of the Society of Antiquaries of Scotland. 113: 449–56. Retrieved 10 October 2015.
• Rees, S.E. (1983). "A wooden ard-share from Dundarg, Aberdeenshire, with a note on other wooden plough pieces" (PDF). Proceedings of the Society of Antiquaries of Scotland. 113: 457–63. Retrieved 15 October 2008.
• "Dundarg Castle". Canmore. Historic Environment Scotland. Retrieved 10 October 2015.
• Simpson, W. D. (1954) Dundarg Castle. Aberdeen University.
• Simpson, W. D. (1960) 'Dundarg Castle reconsidered', Transactions of the Buchan Field Club 17(4), pp. 9–25.

57°40′26.59″N 2°10′39.03″W / 57.6740528°N 2.1775083°W / 57.6740528; -2.1775083