Each of these photographs is of a microscopic castle etched onto a single particle of sand.
Muniz would draw a castle and project it through a special prism.
Then Coelho would trace the drawing onto each particle using a Focused Ion Beam. Each line etched is only a tiny fraction of the width of a human hair.
The entire project took Muniz and Coelho four years. This video shows the mind-bogglingly intricate process in more detail.
If you're in Israel, you can check out these 'sandcastles' at the Tel Aviv Museum of Art.