While surfing the net I found a few interesting pictures -- I know what is done but I won't reveal the wonder.... If you guess it, keep it to yourself.
Sorry for so much pics (might be a trouble for those with sloooow connection)
Those are all PAINTED rooms. The photos are untouched. No panes of glass, no ropes, no plastics, etc...
Rest in peace, Kym. I hardly knew ya. Rest in peace, Marinus. A bright star, you were ahead of me on my own tracks of thought. I miss you.
Thanks for sharing these amazing pics Muzo. Even if there's an easy technique the rooms would have to be painted with amazing precision.
I saw something a bit similar last month, but with a sculpture in a park, which just looked like odd bits of metal until you saw it from the correct angle, when you could see the numbers 0 - 9.