I just came back from another photo expedition with Bruce to Kaeng Krachan in the Petchaburi Province only about 3 hours from BKK.





Here is some brief info on the park I found from Wiki:

Geography

The park covers parts of the districts Nong Ya Plong, Kaen Krachan and Tha Yang of Phetchaburi Province, and of Hua Hin of Prachuap Khiri Khan Province. It consists mainly of rain forests within the eastern slope of the Tenasserim Mountain Range. The highest elevation is at 1200m, the mean elevation of the area is at Two main rivers originate within the park, the Pranburi River and the Phetchaburi River.
The Phetchaburi is blocked by the Kaeng Krachan dam at the eastern border of the park. The dam creates a lake covering an area of 46.5 kmē. The dam was built in 1966.
History

The park was created on June 12 1981 as the 28th national park of Thailand. Originally covering an area of 2,478 kmē, it was enlarged on December 27, 1984 to include the boundary area between Phetchaburi and Prachuap Khiri Khan provinces.
The park has been included in the list of ASEAN heritage parks. In 2005 it was also submitted to UNESCO for consideration as a future world heritage site.
Fauna and Flora

The forests contain a very diverse collection of tree species, both continental trees like oaks, chestnuts, and maples, but also trees found on the Malay Peninsula like palms.
57 species of mammals and more than 400 bird species had been counted in the park.