The main tourist site in Camodia is the Angkor Archaeological Park and is more commonly known as Angkor Wat. So much so that the temple has been incorporated on to the national flag. The area encompasses some 400 square kilometres, so to really explore it you need at least three days.
However if time is of the essence then there is a slimmed down version that covers the main highlights and can be done is a day.
On the 'small tour' the essentials are of course - Angkor Wat, then Angkor Thom, Ta Prohm and Banteay Kdei in the return to Siem Reap.
Here are some of my favourite view of the area.