Phraya Nakhon Cave is the standout attraction of Khao Sam Roi Yot National Park, famous for the striking royal pavilion (Phra Thinang Khuha Kharuhat) inside its massive main chamber. Built in 1890 for visits by King Rama V, the pavilion has become a symbol of Prachuap Khiri Khan Province. The cave consists of two large sinkholes, allowing sunlight to illuminate the pavilion - a truly magical sight when the light falls at the right angle around 10:00-10:30 AM. Reaching the cave requires a moderate hike of about 430 meters up steep, rocky trails.