Khao Sam Roi Yot National Park is the strongest nature excursion from Hua Hin: a coastal park of limestone ridges, freshwater marsh, mangroves, beaches, and caves. It is often described as Thailand's first marine national park, and its name, “mountain of three hundred peaks,” fits the jagged skyline that rises abruptly from the Gulf plain.
The main draw is Phraya Nakhon Cave, where a royal pavilion sits under a collapsed cave roof and catches a shaft of morning light. The park also works for birdwatching, boat trips, and short hikes, but distances between sights are large enough that having your own transport or a driver makes a real difference.