The castle is open daily in the summer from 10am to 6pm. We visited Viandan Castle on Sunday, the 14th of August, which was one day before a religious public holiday (Mary's Ascension). Therefore, the castle had one of its biannual medieval festivals. Tourists of all ages and from all over Luxembourg congregated here to watch the medieval dancers, cobblers, ironsmiths, monks, and knights. Of course, this was very cheesy, but I was taken in by the festival's charm and magnificent castle.
Vianden Castle was constructed between the 11th and 14th centuries on the foundations of a Roman "castellum" and a Carolingian refuge. This castle, as well as the city of Viandan, had the look and feel of a fairy tale. Until the beginning of the 15th century, it was the seat of the influential counts of Vianden, who were connected by marriage to the royal family of France and the German imperial court.