Khao Yai rewards active visitors. Hiking trails range from short riverside walks to full-day treks through jungle and grassland, and the birding is among the best in Thailand — bring binoculars even for a short walk, with a good chance of spotting several of the park's four hornbill species. Night safaris along the park roads give the best odds of seeing civets, porcupines, and other nocturnal wildlife, and occasionally an elephant caught in the spotlight. The waterfalls are a highlight too — Krok E Dok on the western side of the park is a demanding rainy-season hike, at its best when the trail is muddy and the cascades are running strong.
Trails aren't always clearly marked, so a guide is worth it for anyone serious about wildlife-spotting rather than just a walk in the woods — several Bangkok- and Pak Chong-based operators run day and multi-day hiking, birding, and photography tours into the park.