Towering over the Altstadt, Heidelberg’s ruined Renaissance castle cuts a romantic figure, especially across the Neckar River when illuminated at night. Along with fabulous views, attractions include the Deutsches Apotheken-Museum. The castle is reached either via a steep, cobbled trail in about 10 minutes or by taking the Bergbahn (cogwheel train) from Kornmarkt station. The only way to see the less-than-scintillating interior is by tour. After 6pm you can stroll the grounds for free.