Trim Castle covers 30,000 square metres on a rise above a ford of the Boyne and is the largest Anglo-Norman fortification in Ireland. Hugh de Lacy began it around 1172 as the centre of his Lordship of Meath; the first timber ringwork was burned by the Irish high king Ruaidrí Ua Conchobair, and the stone castle was finished by his son Walter in the 1220s. The three-storey keep is cross-shaped with twenty corners, a design found nowhere else in Norman building. A long curtain wall, a barbican gate and the remains of a moat surround it.
The castle grounds are free to explore on your own, with interpretation panels; the keep is visited only on a guided tour, with steep, narrow stairs and walkways that let you look down into its hollow interior. The castle played York in Braveheart. The Office of Public Works has announced a closure for works from 1 November 2026 to 1 April 2027, so check before you go.