More than 18 million Geronimo Stilton books in print! Finally, I was about to leave for a relaxing vacation all by myself. I was ready to kick back and connect with nature. But somehow, my peaceful trip turned into a crazy treasure hunt in the beautiful Black Hills of South Dakota with the entire Stilton clan in tow! Our journey even included a hot-air balloon ride to Mount Rushmore. Holey cheese! This was one adventure I'd truly remember.