I build up castles. I tear down mountains. I make some men blind, I help others to see. What am I?

Common Wrong Answers
“Water”
While water can erode mountains and is essential for life, it does not literally build castles or make men blind.
“Wind”
Wind can erode mountains and affect visibility, but it does not build physical structures like castles or help others to see in a literal sense.
“Light”
Light can help people see and can cause blindness, but it does not build castles or tear down mountains.
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