Rindoon, the lost town
In 1227 a castle went up on St John's peninsula, jutting into Lough Ree on the edge of Norman-held territory - the work tied to Geoffrey de Marisco and the Anglo-Norman push up the Shannon. A town followed: a walled settlement of perhaps a thousand people, with a parish church, a hospital run by the Fratres Cruciferi, a mill and a harbour, trading between the Norman river towns and the Gaelic country beyond. A town wall close to two kilometres long was thrown across the neck of the peninsula, with a gatehouse and towers. From 1229 it was attacked again and again, and with the Gaelic resurgence of the fourteenth century it was sacked and slowly emptied; by 1342-3 it was described as in Irish hands. It was never rebuilt. What survived is extraordinary - castle, wall, gateway, a later windmill on the church tower, the church and graveyard - sitting in farmland with the lough on three sides. Some call it the Camelot of the Shannon. Access is across private land and has been on-and-off closed, so check first.