More formally known as the Cathedral Church of St Deiniol, this building occupies one of the oldest ecclesiastical sites in Britain, dating from AD 525, when the saint founded his community here. The beginning from which the city of Bangor grew, today's stone church dates to the 12th century, when Gruffudd ap Cynan rebuilt it following Viking raids. Later episodes of destruction followed, and much of today's cathedral is the work of Victorian architect Sir George Gilbert Scott.
The cathedral has a small shop and an exhibition about its history. An artistic highlight is the late-15th-century, almost life-size, oak carving of Christ, seated and shackled in the moments before his crucifixion. A stroll in the adjoining Bible gardens is pleasant, despite the depredations of thieves (the gardens previously contained examples of all plants mentioned in the Bible).