A substantial ruin located on the edge of Culzean Country Park, 1¼ miles (2 km) north of Kirkoswald in South Ayrshire, Thomaston Castle comprises a 16th century L-plan tower-house of three storeys. It would originally have had a garret above a corbelled-out parapet. The entrance was in the square stair tower which occupies the re-entrant angle between the two blocks. Recorded as Thomastoun on Johann Blaeu's Atlas of Scotland (1654), this tower-house was built within a 13th C. courtyard castle of some importance, which was said to have been built by Thomas Bruce, a nephew of Robert the Bruce (1274 - 1329). The property passed to the Corry family of Kelwood in 1507, and they built the tower. This includes a vaulted basement which once contained a kitchen and wine cellar. An arched pend through the basement of the SE-facing wing gave access to the former walled courtyard to the south. The hall was on the first floor, with bedrooms on the floor above. Around 1632, the castle passed by marriage to the MacIlvaines (or McElwain) of Grimmet and remained in use until c.1800. The ruins are B-listed and are a scheduled ancient monument.