Up there on the podium with some of the world’s greatest parks, Khao Yai is Thailand’s oldest and most visited reserve. Covering 2168 sq km, Khao Yai incorporates one of the largest intact monsoon forests remaining in mainland Asia, which is why it was named a Unesco World Heritage Site (as part of the Dong Phayayen–Khao Yai Forest Complex). The mostly English-speaking staff at the visitor centre are very friendly and helpful.