Riddle: I build up castles. I tear down mountains. I make some men blind, I help others to see. What am I?
First of all, people have been using sand to build castles since the ancient times.
Second, sometimes sand can destroy things. It could even tear down mountains or mountains can erode into sand.
Third, in sandstorms, a meteorological event common in arid and semi-arid regions, sand can cause people to go blind if it gets in their eyes.
Finally, glass production is made using silica in sand form, soda, and lime. As you can see, silica in the form of sand is one of the main ingredients in the construction of glasses. In this way, it helps people with vision problems to see. The answer of this riddle is sand.
Answer: I am Sand.