The Castle of Sancti Petri is a historic fortress located on the island of Sancti Petri, just off the coast of Chiclana de la Frontera in Spain. Built in the 17th century, the castle offers stunning views of the surrounding area and the Atlantic Ocean. Visitors can explore the castle's interior, which houses a small museum showcasing the history of the fortress and the island. The castle is also a popular spot for birdwatching, as it is located in a nature reserve known for its diverse bird species.