Angkor Wat - One of the UNESCO World Heritage sites.
It has impressive monuments and ancient sculptures and very unique setups. Like tree growing on top of the building?!
But sadly, many of the temples are left of remains, and undergoing certain restoration.
Better go see before not much of the original remain there.
It's located at Siem Reap, from town, you can book any tuk tuk for the whole day to travel to different temples ... We got ours at $15USD for the whole day which was okay for us.
Note the entrance fees below:
$20 for 1 day pass
$40 for 3 days pass (1 week validity)
$60 for 7 day pass (1 month validity)
There are many temples so you cannot cover so many especially with the hot sun...
We did the main Angkor Thom temples, including Bayon, and Ta Phrom.