Craigmillar Castle takes us back to the 14th Century when the castle tower was first constructed, followed by the courtyard walls in the next century. The castle has a history of murderous events and is also where Mary Queen of Scots retreated in the 15th century.
This location was the ideal stronghold to shoot the scenes for Ardsmuir Prison thanks to its decaying exterior, so there was hardly any adaptations needed to use the castle for filming. From the series, we see Ardsmuir Prison as having a Scottish Highlands setting, although no filming ever took place in the Highlands. This is the setting where Jamie, Murtagh and several Jacobite dissidents are incarcerated following the Battle of Culloden in 1745.