Hundreds of “windows” like this can be seen throughout the Angkor Archaelogical Park, in many of the temples and in various states of repair. The above angled view was captured at Angkor Wat and (as the most famous temple) it has been repaired the most, you will notice that the third from the left column has been completely replaced where others appear much older.
There was also a difference in colour of the stone, but I liked the pattern more and thought it would make a better final photograph converted to black and white, focusing the eye on the texture of the stone bars.