This sober library (1712-1732) is by Thomas Burgh, chief engineer and surveyor general. The wonderful treasury includes some of the library’s most important works including the extraordinary Book of Kells, and illuminated manuscript on vellum (c 800), recounting the Gospels in Latin. In the impressive Long Room (64m by 12m), don’t miss the oldest surviving Irish harp, at least 500 years old and an emblem of the nation.