Maybe you could put exposed, damaged holopanels in the simulation? Like walls of sparking panels that appear to be hanging in mid-air at the edges of the simulation because they are malfunctioning? It could flicker between displaying the sky and the panels too.
You could have a lot of fun too, how about a simulation of E1M1? I heard you like Doom, so I put Doom inside Doom so...
Or you could enter the simulation, only to find it is a simulation of the area where you enter the simulation. We have to go deeper...
