Have a look at the  3 day tour that concentrates on the Angkor Temple complex and a 4 day tour that takes you to both the Angkor Temple complex and surrounding area. This will give you an idea of what sights to cover during your stay there.

Siem Reap is easily accessible from Thailand and it makes an ideal extension to your Thailand tour. There are flights from Bangkok directly to Siem Reap more than once a day. The flight takes 1hr.

For a 3 day tour of the Angkor Wat complex, see the tour:
The Wonder of Angkor Wat.

For a 4 day tour of Angkor Wat and the surrounding area, see the tour:
Angkor Wat Exploration

The amazing ceremonial temple complex at Angkor was discovered by French naturalist Henri Mouhot in 1860 when he came upon the ruins of Angkor Thom, the ancient Khmer capital, situated near present day Siem Reap. The most famous & best-preserved structure is Angkor Wat; a series of temples built between 1112 & 1152. Its layout is breathtaking: a giant moat surrounds the main structure & a huge stone bridge traverses it. The moat, said to represent the oceans of the world is nearly 200 metres wide; the wall surrounding the enclosure measures 1,000 meters by 800 & the central tower rises 55 meters from the ground. Once inside the outer walls you are dazzled by an array of beautiful bas-reliefs and ornate carvings depicting various scenes from Hindu epics such as the Ramayana and Mahabharat.

The Khmer Empire spanned a period of approximately 600 years, its zenith being in the first half of the 12th century when Angkor Wat was constructed. The founding kings of the 9th century regarded themselves as God Kings, or Devaraja, with divine powers. This led to the creation of the temples, dedicated to the worship of the Khmer kings. One of the oldest is at Roulos, east of Siem Reap. Here King Indravarman created a reservoir, or Baray & established Preah Ko , both of which survive to this day. His son chose to build on a nearby hill known as Phnom Bakheng; today this five-tiered temple is a popular place to watch the sunset.

Angkor Thom's classical age began in the 11th century when The Khmers conquered much of present day Southern Laos and Thailand. Further conquests over the next century meant that the Khmer kings had the resources and the manpower to embark on their most ambitious building program, Angkor Wat. By the time it was completed, Angkor Wat had a population of 750,000. Ironically, within 25 years of its completion, the Kingdom was over run by the Chams of southern Vietnam. The Chams victory was short-lived but its effects were profound. The king responsible for evicting the Cham , Jayavarman VII adopted Buddhism as the national religion & embarked on a bold series of building projects , including the walled city of Angkor Thom with the Bayon as its centerpiece.

The Bayon is characterized by its’ giant sculptured heads. Set in the heart of Angkor Thom, it is a bizarre structure with a total of 54 towers elaborately decorated with over 200 enigmatic smiling faces. The fortified city of Angkor Thom covers an area in excess of 10 square kilometers with 12 kilometers of wall, complete with a moat thought to have originally contained crocodiles. Not long after the death of Jayavarman VII the empire began to fall into terminal decline and within 200 years of Angkor Thom’s completion the entire city was abandoned to the jungle where it lay hidden until a young Frenchman's "discovery".