St. Patrick's Cathedral is the site of a holy well used by St. Patrick for baptisms. A church was established there in the late fifth century. A stone marking the well was found in 1901.
The present-day cathedral was founded in 1192 by Archbishop John Comyn. He lived in the priory of Christ Church Cathedral. He didn't agree with the city laws, so he started a cathedral and palace outside the city walls.
St. Patrick's is one of the largest cathedrals in Ireland. It is 91 meters long. Jonathan Swift, the author of Gulliver's Travels, was Dean of the cathedral for many years, and his portraits show St. Patrick's in the background.
St. Patrick's Cathedral looks like this from the outside.