Hanoi Project Facility
While an important structure, the facility itself is nondescript, being a simple stone building. The chambers where the six test subjects of the Hanoi Project; Jin Kolter, Miyu Sugisaki, Windy's partner, Spectre, Theodore Hamilton and Yusaku Fujiki, were kept were apparently located next to one another, though the children never heard nor knew of each other's presence. The rooms could deliver food to the children if they won their Duels via mechanical arms. The children generally had little contact with anything beyond the processes they were subjected to, with the exception of Yusaku and Jin; Yusaku was often consoled by Roken Kogami to help him survive, while Jin was tormented by the Ignis created from him, Lightning.
With the exception of the rescue of the six children, the facility is often seen during the rain; Roken finds Spectre there in a rainstorm and Varis later had it rain at the digital recreation of the facility in LINK VRAINS until Soulburner finally made peace with his past.