Planning a trip and wondering Is Gibraltar a country? Gibraltar also is known as “the Rock” is a British air and naval base that guards the Strait of Gibraltar, which is the only entrance to the Mediterranean Sea from the Atlantic Ocean. The peninsula consists of a limestone and shale ridge (the Rock), which rises abruptly from the isthmus to 1,380 feet (421 meters) at Rock Gun, its northernmost summit. Its highest point, 1,396 feet (426 meters), is attained near