Angkor Wat, Cambodia.
"It is of such extraordinary construction that it is not possible to describe it with a pen, particularly since it is like no other building in the world. It has towers and decoration and all the refinements which the human genius can conceive of."
-Antonio da Magdalena, 1586.
Angkor Wat still functions as a place of Thereveda Buddist worship, making it one of the largest and oldest spiritual temples on Earth still in use (continuously).