Penmon was founded by Enion, Prince of Llyn, and Seiriol was his younger brother. Seiriol was appointed the head of the community. The saint lived as a hermit between his cell next to the holy well, and a church built on the island known as Ynys Seiriol. The present church was built in the twelfth century that replaced a church that was burnt down by the Vikings. Later in the thirteenth century Penmon became an Augustinian friary, and the ruins of the priory buildings still dominates the site.

Pilgrims can visit the church, holy well and see the original cell foundations, monastery refectory, fishpond and dovecot. Inside the church there are two tenth century stone crosses with detailed interlace patterns with Irish and Scandinavian style carvings.

When you travel further down to Penmon Point you can see over to Ynys Seiriol and its tower marking the site of Seiriol’s hermitage.