Proof of Trim's medieval importance, this remarkably preserved edifice was Ireland's largest Anglo-Norman fortification. Hugh de Lacy founded Trim Castle in 1173, but it was destroyed by Ruaidrí Ua Conchobair, Ireland's last high king, within a year. The building you see today was begun around 1200 and has hardly been modified since.
Entertaining guided tours involve climbing narrow, steep stairs, so aren't suitable for very young children or anyone with restricted mobility. Self-guided tours are also available.
Throughout Anglo-Norman times the castle occupied a strategic position on the western edge of the Pale, the area where the Anglo-Normans ruled supreme; beyond Trim was the volatile country where Irish chieftains and lords fought with their Norman rivals and vied for position, power and terrain. By the 16th century, the castle had begun to fall into decline and in 1649, when the town was taken by Cromwellian forces, it was severely damaged.
The castle's grassy two-hectare enclosure is dominated by a massive stone keep, 25m tall and mounted on a Norman motte. Inside are three levels, the lowest divided by a central wall. Just outside the central keep are the remains of an earlier wall.
The principal outer-curtain wall, 450m long and for the most part still standing, dates from around 1250 and includes eight towers and a gatehouse. It also has a number of sally gates from which defenders could exit to confront the enemy. The finest stretch of the outer wall runs from the River Boyne through Dublin Gate to Castle St.
Fans of the film Braveheart might recognise it as Edinburgh Castle, York Castle or the Tower of London (it starred as all three).