"Yui-onēsama, your vision was obscured by the handkerchief, so
you probably didn’t see it, but my eyes did. The hotel flipped over
with the surrounding ground."

"Flipped over?"

We turned back to the original location of the hotel, and found
that there was a very small gap between the footing of the hotel
perimeter wall and the ground. According to her, the entire hotel
was originally located on a piece of something similar to a thick
board, and in the center of this board, there was a rotation axis
that ran through the entire thing, and so, the board rotated 180
degrees like a stage, becoming an empty space. That was the
mechanism of it. The walls were used to cover the cracks in the
ground.

"When the locked room murders occurred in the hotel, Yuionēsama once suspected that the walls might be able to rotate.
But in fact, the walls weren’t what can rotate, but the entire
hotel."

Shinsen unfolded the handkerchief in front of my eyes to
temporarily hide this mechanism, which is a common blinding
technique used by magicians and illusionists.

"To make an object of that mass flip smoothly without making a
single sound requires a device of unimaginably large scale. Maybe
the buildings related to the ‘Black Challenge’ are all able to
instantly disappear from sight through a variety of methods, and
usually they are hidden, only appearing when the game begins."

"Then how do you explain the fact that everything around them
fold up and disappear?"

"I think they just fold up and disappear too. They are basically
things like set boards or paper models that can be recycled at any
time. The ‘Black Challenge’ is essentially a kind of show, so it's not
surprising that everything is a stage set including the
background."

Despite what Kirigiri said, I still found it unbelievable. The Crime

Victims’ Relief Committee offers all kinds of crimes in all kinds of
places. Does it all require the large-scale installations and setting a
backdrop? It feels like no amount of funding would be enough for
that.