The white facility is the building where an important part of Euphoria's plot occurred.
Architecture
This facility is a complex underground building composed by a lot of nearby identical white room with a few exception as the "main room" or the VIP room they consist in a gigantic maze for anyone that doesn't know the place very well. According to Keisuke, this facility looks like an hospital. Every round is linked to other by automatic door thar are lighted in red when they are close and green when they open up. The facility is constantly lighted by ceiling light, giving the impression that everyting is white. The entirety of the floor and even the wall are covered up by white slabs. The main room is described as quite large, large when the other rooms are smaller (large enough for 7 people to be inside at the same time).
The White facility possesses a secret passage that lead to an undergroud tunnel. It is hinted that they are different entrance and exit for the underground, but only one is known, it makes an exit close to a forest near to the Rokukeikan Academy.
Spoiler alert
It is said that they are different floor in this facility (at least two). Far deeper underground than the first floor, there is a second floor where is located Rakuen and the sleeping beauty.
We also know that they were another exit to the white facility that leads to Keisuke's secret base (an area where he could play) when he was young. However, Keisuke blocked this entrance to the white facility because he wanted that no adult could come in his secret base.