Italian artist Michelangelo Roberti is making 999 black cubes (20 cm each side) and selling them on his website saying that there is something different inside each one but DON'T OPEN IT! He also says:
"In this deep sense the thing inside the cube is a representation of the Absolute. A good definition of Absolute can also be 'something that doesn't draw its reality from the fact of being perceived'. Curiosity is paradoxical and comes from the useless hope to perceive the Absolute."
Also a nice interview with him here