Harjukaupungin salakäytävät refers to the underground tunnels located in the city of Harjukaupunki, Finland. These tunnels were originally constructed for various purposes, including transportation and storage, and have become a point of interest for both locals and tourists. The tunnels are known for their historical significance and unique architecture. They provide a glimpse into the city's past and are often explored during guided tours, showcasing the engineering techniques used during their construction and the role they played in the development of Harjukaupunki.