Chanthaburi

Of all provinces in the eastern coast of Thailand, Chanthaburi is lesser known to tourists, partly due to its 250 kilometre distance from Bangkok. However, that does not mean it lacks the beauty a good beach destination has.
Perhaps unknown to many tourists, Khung Wiman Beach, Khung Krabain Bay, Laem Sadet Beach and Chao Lao Beach are both peaceful and picturesque. Their scenic beachside roads are featured in several TV commercials.
BeachesKhung Wiman BeachThe most scenic beach in Chanthaburi, Khung Wiman has a beautiful beachside road that goes along a fine brown sandy beach and winding hillside roads. The beach is flanked with pine trees while the water is clear and good for swimming. It is considered one of Thailand’s most beautiful beachside roads and often used in TV commercials in Thailand.

Next to Khung wiman Beach is Khung Krabain Bay. It is the site of Chanthaburi’s verdant mangrove forests and the Khung Krabain Study and Development Centre under Royal Patronage. You can explore the mangrove forest via an 850 metre-long wooden bridge. Spare at least half an hour.
Laem Sadet BeachLocated opposite Khung Krabain Mangrove Forest, Laem Sadet beach stretches 3 kilometres long on a white sandy beach. The bay is shady with pine trees and fine for swimming. There are a few resorts on this beach.
Chao Lao BeachLocated east of Khung Krabain Bay is Chao Lao Beach. The beach is popular among locals who come here on weekend. It boosts brown sandy beach and shallow water suitable for swimming. There are some good resorts by the beach.

Reference : http://www.circleofasia.com/Chanthaburi-Thailand.htm