The Waterford Crystal Visitor Centre is at the House of Waterford Crystal on The Mall, about 500 metres from the Viking Triangle. Tours take you through the full production process — blowing, cutting, and engraving — with working craftspeople demonstrating each stage. The gallery upstairs holds the world's largest collection of Waterford Crystal, including pieces made for the White House, the Vatican, and various royal households.
The factory tour is genuinely interesting even for people who aren't particularly interested in crystal: the skill involved in the cutting and engraving is impressive to watch, and the guides are knowledgeable about both the craft and the history. Tours run throughout the day on weekdays; weekend tours are available but less frequent.
The gallery and shop are free to enter; the factory tour carries a charge.