Rough Castle is one of the most complete Roman forts in Scotland, a rectangular earthwork defended by multiple ditches cut into the ground west of Falkirk. The outer defensive pits — called lilia — are still clearly visible, and the sheer depth and regularity of them gives a real sense of the effort the Romans put into making this a defensible position. The site is in the care of Historic Environment Scotland and is freely accessible.
The fort sits on a stretch of the Antonine Wall, which you can walk along through the surrounding farmland. The wall itself was an earthen rampart rather than stone — unlike Hadrian's Wall further south — so what you see here is a grassy bank, but the context and the fort's earthworks together make this one of the better Roman sites in Scotland. Access is via a farm track from Bonnybridge, about five kilometres west of Falkirk town centre.