Phetchaburi is at the north end of the Malay Peninsula, with the Gulf of Thailand to the east and the Tanaosi mountain range forming the boundary to Myanmar. Except for these border mountains most of the province is a flat plain. With an area of about 3,000 km² the Kaeng Krachan National Park is Thailand's largest national park, covering nearly half of the province.[2] It protects mostly rain forests in the mountains along the boundary to Myanmar, but also the Kaeng Krachan Reservoir is part of the park. The only significant river of the province is the Phetchaburi River.