Schloss Heidelberg (Heidelberg Castle), Heidelberg (must see)

The romantic ruins of this old castle rise over the town, creating a picturesque scene. Built and expanded multiple times between the 13th and 17th centuries, it was originally a heavily fortified Gothic stronghold and the seat of the House of Wittelsbach palatines. In the 16th century, the complex was remodeled into one of Germany's most stunning residences, but its glory was short-lived due to the devastation of the Thirty Years' War and the 1689 war with France, during which most of the structure was destroyed and never rebuilt.

What's most striking here is the architectural variety. The oldest parts still standing date back to the 15th century, though most of the castle was built during the Renaissance in the 16th and 17th centuries when it was the seat of the Palatinate electors. There's an "English wing" built in 1612 by Elector Friedrich V for his teenage Scottish bride, Elizabeth Stuart; its plain, square-window facade stands out against other, more opulent styles. The architectural highlight remains the Renaissance courtyard—harmonious, graceful, and ornate.

Even if you have to wait, make a point of seeing the two-story Great Cask ("Grosses Fass") in the cellar, possibly the world's largest wine barrel, made from 130 oak trees and capable of holding 58,500 gallons. It was used to store wines paid as taxes by wine growers in the Palatinate. Also included in your ticket is the German Pharmacy Museum ("Apotheken-Museum"), where you can see six re-created apothecaries dating back as far as the 17th century, complete with a collection of books, medical instruments and medicine bottles.

In summer there are fireworks displays, on the first Saturday in June and September and the second Saturday in July, to commemorate when the castle went up in flames in 1689, 1693, and 1764 (two of the fires happened during wars with the French, and the last one was caused by lightning). June and July also feature a theater festival, with performances of "The Student Prince" often taking center stage.

Tip:
Skip the hike up the Burgweg and take the Königstuhl Bergbahn (funicular) instead—it's faster and less tiring!