Cahill City is a fictional location featured in the popular book series, The 39 Clues. It serves as a central hub for the adventures of the Cahill family, a powerful and influential lineage. The city is known for its rich history and connection to various clues that lead to hidden treasures and secrets. In the series, Cahill City is depicted as a vibrant urban area filled with landmarks and locations significant to the Cahill family's legacy. The city plays a crucial role in the characters' quests, as they navigate through challenges and puzzles to uncover their family's past and the mysteries surrounding it.