Semiran Castle in Qazvin County, Qazvin Province, Iran, is a historic fortress known for its impressive size and architectural design, covering about 5,300 square meters. The castle showcases a blend of military strength and aesthetic beauty with massive stone walls, circular defensive towers, and decorative elements like brickwork and plaster molding. Its entrance is notable for a large gateway built into the southwest tower.

The castle has undergone multiple restorations over centuries, especially during the Safavid and Qajar periods, reflecting Iranian creativity and architectural heritage. It has served various functions throughout history, including as a residential palace and military stronghold, maintaining its prominence in the region's cultural landscape.