Brown's next book was supposed to be called "The Solomon Key", but then the name was changed to "The Lost Symbol". When the book "The Da Vinci Code" came out in the United States, there were some puzzles hidden in the art of the book cover. Brown said that the answers to those puzzles give hints about what would be in his next book. Two of the puzzles are about a famous sculpture called "Kryptos", which is in the middle of the CIA Headquarters building in Washington D.C.