The center of British power in Ireland for more than 700 years, this 13th-century castle was finally taken over by the new Irish government in 1922. You can wander the grounds for free, but they’re somewhat plain—the police and government agencies use a significant section of the castle as office space. You'll need to take a guided tour to see the impressive State Apartments, the early 18th-century Treasury, and the Gothic-style Chapel Royal, with its fine plaster decoration and carved-oak gallery. The castle’s only extant tower—a 13th-century structure once used to imprison suspected traitors—now holds a small museum dedicated to the Garda. In 1583 the castle’s Upper Yard was the scene of Ireland’s last trial by mortal combat; today it is dominated by an impressive Georgian structure called the Bedford Tower. The Irish crown jewels were kept in the tower until they were stolen in 1907 (they have never been recovered). If it’s open, check out the Medieval Undercroft, an excavated site on the grounds where an early Viking fortress once stood. Note: This is a government building, so some areas may be closed for state events.