Nakhon Nayok province
Khao Yai National Park, the first national park of Thailand was declared a national park on September 18, 1962.  It covers areas of four provinces: Nakhon Nayok, Nakhon Ratchasima, Prachin Buri, and Saraburi.  The park occupies an area of 2,168 square kilometers and consists of virgin forest, tropical forest, streams, waterfalls, wildlife, and a variety of plants.  The most suitable visiting time is during the Thai winter, from October to February when it is cold at night until the next morning.  The highest point is Khao Rom Peak, which is 1,351 metres above sea level.