The original Thirlestane Castle - where Thomas de Thirlestane lived lies about 2 miles south east of Thirlestane Castle in Lauder. Thomas came from the old Northumbrian nobility, and also held a castle at Abertarff on Loch Ness. He died in 1228, defending the castle at Abertarff. His widow, Agnes, held both Thirlestane and Abertarff in her own right for the next 25 years or thereabouts, until Richard Mautalent, a younger son of the Mautalents of Northumberland, married her daughter Avicia some time after 1250. 

Agnes was clearly a formidable and capable lady, and also, we think, very well connected, because it was unusual at that period for women to hold one military fief, let alone two. Old Thirlestane, just outside Lauder,  was part of the Morville fief covering much of south east Scotland, excluding Lauder itself, which was held by the Lauder family. 

It was here that Richard Mautalent (Auld Maitland) lived when he married Avicia. This was "the darksome tower" he defended for several weeks against English forces under Edward I around 1296.

It was very uncomfortable and small, with three floors and one room per floor  and the Maitlands had made Lethington (now Lennoxlove) their principal residence by sometime after 1300

To find the tower, take the road from Lauder to Greenlaw & Duns.