[Argus25]

Originally Posted by julie_m

How about using half-silvered glass? With no illumination from within, and therefore nothing to transmit (any light coming in through one of the half-silvered panels and out of one of the others will be doubly attenuated, once on the way in and once on the way out), it would just look like a plain mirrored box. Switch on some bright lights inside the box, though, and you would be able to see the insides clearly, the transmitted light swamping out the reflection.

Then you will end up with a David Copperfield style magic show.