This imposing library (1712-32) is by Thomas Burgh, chief engineer and surveyor general of fortifications. The wonderful treasury includes some of the library's most valuable works, including the extraordinary Book of Kells (c 800), an illuminated manuscript on vellum, on which the Four Gospels are transcribed in Latin. In the impressive Long Room (64m by 12m), be sure to take a look at the oldest surviving Irish harp, which is at least 500 years old.