Orchardton Tower, Palnackie.

This round tower, built by the Cairns family in the mid-15th-Century, was located at the north east corner of a fortified yard or barmkin, which would have sheltered livestock and provided cellars, a bakehouse, and probably a hall built on an upper level. The tower itself, uniquely circular, was reserved for living quarters, and was accessed via a stair, possibly moveable, from the barmkin up to a first floor doorway. The present entrance, on the north of the tower, was constructed in the 17th or 18th centuries. A new door was formed from a window and a permanent stone stair constructed. The Historic Scotland website  has full details.