The monastery is believed to have been founded by St. Seiriol in the 6th Century, near a holy well, and there's evidence of 10th Century prosperity (destroyed by Vikings in 971), but the current buildings, an Augustinian priory, date from the early 13th Century.
Following Dissolution in 1538, the complex was acquired by the Bulkeley family, who built the 'domed' dovecote visible on the right, converted the prior's lodgings into the cream-coloured house adjoining the church (which remained, and remains, the parish church) and used the grounds as a deer park. Most of the remaining ecclesiastical buildings have fallen into ruins, though they're now preserved as such for the nation.

Ynys Seiriol (Puffin Island) is in the background.