Founded in 1592 by Queen Elizabeth I, Trinity College is Ireland's oldest and most notable college. Among its alumni are such renowned writers as Jonathan Swift and Oscar Wilde. Today, visitors from around the world come to explore the college's verdant campus and towering Gothic-style halls.

But the real reason to visit is to take a gander inside the Old Library. These hallowed halls house an amazing collection of literature. Of all the books at the Old Library, the most famous and priceless one is the "Book of Kells." This illustrated version of the gospels was created around A.D. 800 by Celtic monks. The manuscripts' pages come to life with vibrantly hued depictions of Christ and his followers, bordered by intricate Celtic knots and other designs. Whether or not you're religious, previous visitors agreed that seeing the "Book of Kells" in person is truly a sacred experience. Although some visitors complained of crowds in the library, most agreed the "Book of Kells" is a must-see. For a more in-depth visit, consider signing up for one of the best Dublin tours, which stop here.

Like any college campus, Trinity College – located south of the Liffey in central Dublin – buzzes while classes are in session, and you don't have to pay to walk around. The Old Library, however, is a different story. It's open to the public, though hours vary depending on the season. Generally, it's open from 8:30 a.m., 9:30 a.m. or noon to 4:30 or 5 p.m. Admission costs between 11 and 14 euros (about $13 to $16.50) for adults, depending on the time of day you visit. Guided tours are also an option (and recommended by past travelers). For more information, visit Trinity College's website.