Bonus castle for today. Here are the ruinous remains of Clonmacnoise castle. Huge chunks of the castle have fallen away intact and just out at odd angles, held together by 700 year old mortar. The castle sits atop very substantial earthworks and guarded a wooden bridge crossing of the Shannon river next to the castle. At the time, this was a much more significant crossing point of the Shannon than Athlone and the large monastic complex of Clonmacnoise lies just next door.