Scrims and a mirror.
I’m no artist, but I made you a diagram to illustrate how it works.
As you are looking into the Endless Hallway from your Doom Buggy, you are looking through scrims, which are basically a thin gauze that you can see through when the light is behind them.
At the very back is a mirror, and in front of the mirror is the “floating” candelabra, which is hanging from thin black wires. The back of the candelabra is painted black so that you don’t’ see the reflection as clearly as you otherwise would.
As you look through each scrim, the image that you see gets just a little hazy (the level of haze depends on how long it’s been since the scrims have been cleaned).You then look into the mirror, which reflects the hall back at you, but since the mirror covers the whole area from wall to wall and floor to ceiling, it appears that the hallway continues. You even see the reflections of the hanging light fixtures, which appear to extend down the hallway.
And since you are looking back through the scrims again, the image gets a little less clear. And finally, your Doom Buggy is in the dark, so you don’t see it at all in the reflection. It just looks as if the hallway is disappearing off into the distance.
(image from DoomBuggies.com forums)