The site dates from the late 13th century; the earliest charter for the lands dating from 1256, but the remains of the building are of 15th- and 16th-century origin.[1]

In 1570, a dispute arose between Gilbert Kennedy, 4th Earl of Cassillis, and Allan Stewart, the succeeding lay Commendator of Crossraguel Abbey, over the ownership of some of the abbey lands and their rental income.... ...Gilbert, with sixteen men,[11] caught Allan Stewart unexpectedly in Crossraguel Woods whilst a guest of the Laird of Bargany,[2] and tricked him [12] into journeying to Dunure. At the castle, he was deprived of his horse and weapons and guarded by six of the Earl's men.[13]

For two days, Gilbert left the commendator to consider his fate and because he was obstinate and refused to sign over the lands and rentals, Gilbert tortured him twice, roasting and basting his feet and body over a brazier in the Black Vault[14] of the castle,[15] aided by his cook, baker and pantrymen.[16] As a result of the torture sessions of the first and seventh days of September 1570,[17] the lands were signed over to Gilbert.

The Commendator was rescued from his confinement by the Laird of Bargany, Allan's brother in law, who arrived with a body of men; first hiding in the chapel and then storming the castle.[18] The rights to the abbey lands were settled, partly by the Earl providing Allen Stewart with sufficient funds to allow him to live 'comfortably' for the rest of his life.[1] In the meantime, he had been taken to the Cross of Ayr where he had denounced the Earl of Cassillis.[19] The Earl was never fully brought to book for his actions by the Privy Council. Allen Stewart never walked again.[20]

The castle's demise began in the mid-17th century. By 1694, the castle was described as "wholly ruined". It is not clear whether this can be linked to the Civil War period, although local tradition suggests that Dunure had been burnt and/or blown up.

https://en.wikipedia.org/wiki/Dunure_Castle