Okinawa is the largest and most important island in the Ryukyu archipelago and the most southerly prefecture in Japan. More than two million holidaymakers visit each year from the main islands to enjoy the sub-tropical climate and the natural beauty of the islands. The archipelago annexed by Japan nearly a hundred years ago was once an independent kingdom. The many cultural differences from the mainland are reflected in the traditional costumes, the music, the handicrafts, the horse-shoe shaped stone graves and the terracotta lions decorating the rooftops. Around a fifth of Okinawa is taken up by the American military base. Sights include: the city of Naha with the Surijo castle, the sub-tropical park near Motobu, the Gyokusendo cave and the island of Taketomi, which is surrounded by an atoll.