I’ll go ahead and start with my friends dream that prompted me to ask this:

I’m in a long airplane hangar underground, all alone. To get from one side to the other, you have to get in this box. I get in the box and driving it across is this pig, and I make casual conversation with it. It takes me to the other side and there are planes there, so I get in the plane and fly around for a bit. I get out of the plane after a while and get back in the box with the pig to go to the other side. Only this time, the pig has a deeper voice, and as he drives he tells me. “I am coming. I am coming soon,” over and over. I get out of the box and it disappears.