What am I?

I can invent dreams or open the skies. It's easy to use me, just close your eyes. What am I?

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I sleep by day, I fly by night. I have no feathers to aid my flight. What am I?

Taken from a mine and then locked up in a wooden case. Never released but used by students everyday. What am I?

I go up when the rain comes down. What am I?