"Perched picturesquely on a rocky hilltop overlooking the city, Heidelberg Castle is enigmatic, romantic, and one of the few castles in Germany that hasn’t been fully restored. Dating back to the 1300s, it served as the seat of the Palantine electors for several centuries. While it expanded substantially during the 16th and 17th centuries, it was plundered and destroyed on many occasions and now consists of mainly Renaissance and Baroque ruins. It’s free to roam the gardens and exterior, but guests must pay an admission fee to visit the interior. Take a guided tour for a historic overview and access to highlights such as the English Wing (built in 1612 by Elector Friedrich V), the graceful Renaissance courtyard, and impressive rooms like the Knight’s Hall and the Imperial Hall. The Grosses Fask (Great Cask) in the cellar is also worth seeing—the world’s largest functioning wine barrel, it’s made from 130 oak trees and can hold some 58,117 gallons of wine."