A Tenshu is the main tower of a Japanese castle, often referred to as the "keep." It serves as the central structure and is typically the tallest part of the castle, designed for defense and as a residence for the lord. The architecture of a tenshu often features multiple stories, intricate wooden designs, and a distinctive roof style, showcasing the artistry of Japanese craftsmanship. Historically, tenshu were built during the feudal period in Japan, particularly from the 16th century onward. They symbolize power and authority, with famous examples including the Himeji Castle and Matsumoto Castle. Many tenshu have been preserved as cultural heritage sites, attracting visitors interested in Japan's history and architecture.