There are 1,700 CGI shots in this film.

The production team built 26 different sets to create the various spaces in the fictional 108-story high-rise building Tower Sky such as the Chinese restaurant and the pedestrian overpass between the two blocks.

Director Ji-hoon Kim spent two years on the post-production for this film.

Director Ji-hoon Kim was inspired by his personal experience of seeing the 63 Building in Seoul for the first time as a middle school student and imagining how it would feel to be trapped inside of it.