Trinity College Library (Dublin, Ireland)

Trinity College Library captivates with its Long Room, holding 200,000 of its oldest books and the 9th-century Book of Kells, attracting 1 million visitors annually—the highest traffic on this list. While cheaper to enter than the Vatican Apostolic Library (#8) by €3 (€14 vs. €17), its collection of 6 million printed works is dwarfed by the National Diet Library (#6), which holds over 45 million items. The library also preserves 30,000 early printed books from before 1800, offering a tangible link to early modern scholarship that few rivals match.