A ruined tower-house located a half-mile (1 km) west southwest of Dundonald in South Ayrshire, Auchans (occasionally Auchans Castle) was built around 1600 by the Wallaces of Dundonald. Originally a three-storey rectangular structure, with a round stair-tower in the centre of the south wall, the a four-storey wing was added to the west by Sir William Cochrane shortly after he acquired the house in 1639. The square stair tower in the re-entrant angle, the top of which was once surrounded by a balustrade, is dated to 1644. Auchans was extended once again by Cochrane in 1669. A round stair-tower, which was added to the northwest at that time, is capped with a corbelled-out square watch-chamber.
The castle passed to the Earl of Eglinton and the last permanent resident was Suzannah, the eccentric widow of the 9th Earl, who entertained James Boswell and Dr. Samuel Johnson here in 1773. The house was divided into workers flats towards the end of the 18th Century but subsequently fell into disrepair. Although the walls are still standing, the roof and floors have collapsed. Ownership has recently returned to the Earls of Dundonald.