"My favorite Letz Go offering is the in-depth Dublin Castle & Book of Kells tour: it lasts about 2.5 hours, lets you see the 1,200-year-old Book of Kells up close while learning about its symbolism and medieval ornamentation, and then explores the grounds and gardens of Dublin Castle—the former seat of British rule in Ireland until 1922; they also run a half-day tour to the Guinness Storehouse and Jameson's Whiskey Distillery (tours from 63 EUR)." - Matthew Kepnes