It's bigger tnan Notre Dame, St. Paul's,and the Blue Mosque it is the ancient temple complex of Angkor Wat in Siem Reap, Cambodia. It amazed me to be able to walk through,around and climb up on these remarkable buildings. One of the most visited sites, and the largest religious sites in the world, Angkor Wat is the home of two million visitors each year. If you arrive jet lagged as I did, it is no trick to get up at 4 in the morning and get out to Angkor Wat from accomodation in Seim Reap(about 5K away). There you will have the privilege of watching the sun rise over the intricately carved buildings as it has been doing for the last nine centuries. The spiritual quality of that experience will stay with you always.Be generous to your guides, the people in Siem Reap Province are among the poorest in Cambodia.
Because the temple complex is so large I would recommend that you take at least 3 days to visit. You will need to be able to drive to some of the sites as they are not all accessible from the main temple. Some of the outlying temples are being rescued from the banyan trees which seem to enjoy growing through walls and ceilings. The trees themselves are worth seeing as they thrive in this jungle enviornment and are enormous.
The quality of the statuary and carvings are remarkable. They provide insight into the early life of this area. The wealthy with the servants, their entertaiments and battles. One scene depicts a battle on the water, with sinking boats and crocodiles lying in wait,no its not a video, it is all carefully carved in the stone walls of the temple. If you can be there at sunrise you will have the treat of watching the carvings all become tinged with its golden rays.