The Castillo de San Juan, also known as San Juan Bautista, is a historic fortress located in San Juan, Puerto Rico. Built by the Spanish in the late 16th century, it was designed to protect the city from naval attacks. The castle features thick walls, a moat, and strategic vantage points, making it a significant military structure of its time. Today, the Castillo de San Juan is a popular tourist attraction and part of the San Juan National Historic Site. Visitors can explore its well-preserved architecture, learn about its history, and enjoy stunning views of the Caribbean Sea.