Cong Abbey is the village's strongest sight: a ruined Augustinian abbey beside the river, mostly 13th century but built over a much older religious site. The cloister, church walls, and carved details are still enough to give the place shape, and the setting is lovely, with trees, water, and stone all close together.
The abbey also carries a bigger story. Rory O'Connor, the last High King of Ireland, spent his final years here, and the famous Cross of Cong was made for the monastery before later ending up in the National Museum of Ireland. The small monks' fishing house over the river is easy to miss, but it is one of the most atmospheric corners of the site.