Thailand's second largest National Park, Khao Yai National Park covers an area of 2,168 square kilometers, of which some 25% is in Nakhon Nayok Province. The remaining areas are in parts of the neighboring provinces of Saraburi, Prachin Buri and Nakhon Ratchasima. Khao Yai was listed as the first National Park in Thailand on September 18, 1962. The highest peak in Khao Yai is Yod Khao Laem, which is 1,292 meters above sea level. Khao Yai is famous for its distinct landscape – dense, virgin forests, streams, waterfalls and high-altitude plains, which are a safe haven for wildlife including several mammal species such as elephants, tigers, gibbons and deer, and over 300 bird species such as giant hornbills and silver pheasants. In addition, the flora and fauna are impressive, with more than 2,500 kinds of trees, plants and flowers.

Attractions in the Park include beautiful waterfalls, and jungle treks, which start in Nakhon Nayok.