This web page by Giorgio Carboni explains how to easily and inexpensively project the view outside your window onto your wall by turning your room into a camera obscura. All you need is some duct tape, posterboard, and a lens.
...it's best if the window faces a view with some activity, it can be entertaining to see cars moving and people jogging upside down across your wall.
From the Upcoming ueue, submitted by Rob H..
I used to do that all the time with a magnifying glass.
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