It looks like these:
It's basicly a thin surfared box that looks like it goes much deeper than it actually does. It has a very cool illusion, and it is very simple built up.
It i has window tint on the top, so the reflective side is facing away from you, you watch trough the visible side. Under that, there are placed some lights, like LEDs, and under there, on the bottom, you have a nomral mirror. This makes an infinite reflective illusion.
It is very simple to build one yourself, and there are many of the on youtube.
Here is a simple on:
Watch Brusspup Infinity Mirror