On the campus of Trinity College ( The oldest college in Ireland) is the library which is home to the Book of Kells. This ancient manuscript is believed to have been written in the 9th century. The ornate writing and illustrations are beautiful, even after all these years. No photos are allowed in the room which houses the manuscript, so you will just have to take my word for it, or travel there yourself.
The Book of Kells is awesome, but not the only thing of beauty in the building. Upstairs is The Long Room. Aptly named, it houses an eclectic collection of books and manuscripts some very old and others, relatively new.