Ballymoon Castle is a National Monument situated 3.5km east of Bagenalstown, County Carlow. The castle is thought to date from the 14th century. The castle is accessible to the public, with access via a small wooden bridge over a ditch, in a field next to the Fennagh road. Visitors can access the castle walls at ground level. Ballymoon Castle as striking as it is unusual comprises a courtyard about 80 feet square, surrounded by granite walls, 8 feet thick and 20 feet high. Square towers project from three sides while a formidable gatehouse is the feature of the fourth. The interior of Ballymoon Castle is now bare but originally featured two-storey structures built up against the inner walls. Ballymoon Castle was most probably built by Roger Bigod or by a member of the Carew family.