A complicated city scape that Akira Tsubaki often visits in his dreams, accompanied by a dream version of his girlfriend Mikoto Urabe. The pair often dance on the roofs of the cities buildings, with robots, machines, steam valves and other dream people watch on.
In the earlier parts of the manga, and all throughout the anime, Tsubaki gets ideas for his relationship while not dancing with Urabe. In the anime, he also had sex with her in his dream.
The City of Dreams was revisited in chapter 91 of the manga at the very start of the two-parter that would end the series.