The man behind the counter at Ptuj Castle suggested I begin my tour at a display of costumes and masks from Slovenian folk traditions and tales. “But I have to warn you,” he said. “Just the other day a man told me it was the scariest thing he’d ever seen.” He shook his head when I laughed. “I’m not kidding. The guy was practically shaking when he left.” Costumes and masks from Slovenian folk traditions and tales are…