I've seen it a couple of times and as far as I can tell there's no big trick to it. Just a bunch of
trap doors and tracks in the floor.
Roll a little dry ice
fog through and "BAM" it's magic. The real magic of those mysterious scenes under the
opera house is just beautiful look. You get distracted by the over all beauty of the scene something simple appears to be a magical trick.
Most big shows like this have their own custom floor that they bring with them on the truck. It installs over the actual
house stage. This allows them to
build all kinds of little tricks into the floor just for the show.
This is assuming you weren't talking about the Vegas show. I unfortunately haven't seen it, but it's really loaded with cool special effects. In that case you may have seen all kinds of crazy stuff. They built the theater for the show. It's a domed theater. They have these cables that run on motorized tracks up the arched supports of the
dome all the way around. These cables are connected to the central
chandelier. They have so much control with this crazy cable
system they can split the
chandelier into three pieces and fly them around the room like flying saucers. It's something else.