Sarıyer Castle is a historical fortress located in the Sarıyer district of Istanbul, Turkey. Built during the Byzantine era, it served as a strategic military outpost to protect the northern coastline of the Bosporus Strait. The castle features robust stone walls and towers, reflecting the architectural style of its time. Over the centuries, Sarıyer Castle has witnessed various historical events and changes in control, including periods under Ottoman rule. Today, it stands as a popular tourist attraction, offering visitors a glimpse into the region's rich history and stunning views of the surrounding landscape.