Most visitors are irresistibly drawn to Heidelberg by its magnificent gothic-renaissance castle but this is one case in which resistance might be useful! Four million visitors a year suffocate this pretty town, so unless you simply can't miss it, go see another castle - there are heaps of them. Heidelberg is also known for its paucity of cheap accommodation and its overpriced food.
That said, the romantic appeal of the castle cannot be denied, and it is possible to escape the tourist hordes by tramping one of the paths in the hills surrounding Heidelberg, stopping now and again to gasp at the view. The Great Vat is also worth a gawk: it holds a neat 220,000 liters! To beat a hasty retreat, there are frequent train connections to Frankfurt, Stuttgart, Munich and elsewhere.