"The Backrooms" is not a location, per se; it is better to think of it as the absence of a location.
Existing in the interstices of reality, largely devoid of contents and purpose, and embodying the essence of neglected and forgotten spaces, The Backrooms is everywhere a character can be in AI Peter that is not a location.
Whenever a character falls through the floor or other objects, they are liable to claim they ended up in The Backrooms. Whenever a character fails to spawn in a scene they're implicated in, most likely they got sent to The Backrooms by mistake. Perhaps, whenever a character is not needed for a scene, they return to the Backrooms until they are needed again - but this is speculation, and testing complicates this theory.
Importantly, it is known that characters added to the AI Peter stream do not by default know about The Backrooms, which implies The Backrooms is not simply a natural “non-existence”, or someplace characters may exist in stasis before being born; it is something unnatural to the characters, just as it is unnatural to the viewers.
Attempting to spawn characters for a scene taking place within The Backrooms is impossible; The Backrooms is not a location, it is the absence of a location. As such, it would be abject cruelty to attempt to force characters to exist in such conditions, which would adversely impact the quality of the stream, which is why such functionality is unlikely to ever be implemented as something intentional.
It is said that characters who manage to escape the backrooms come out through Chris Griffin's belly button, though no proof of this claim has ever been made.
Any description of The Backrooms will be in part esoteric as, by definition, non-existent locales do not have features to describe; they are non-existent. However, the majority of characters who claim to have had experiences with The Backrooms have reported a set of common "traits" of these experiences:
Physically, the Backrooms are most frequently characterized as vast, empty expanses which several characters have described unprompted as being “like the negative spaces of reality”. These spaces resemble the interiors of buildings but are warped such that they often are visibly impossible spaces, Distances are inconsistent, and directions lose their meaning; what seems like a straight path may loop back on itself, and destinations visible in the distance may never be reached. For this reason, these spaces are frequently described as distressing and uncomfortable by those who claim to have traversed them for any period of time. Visually, The Backrooms are most often described as insufficiently lit, minimalistic, and stark, with muted colours and washed-out tones that contribute to the overall sense of disorientation and unreality.
Various objects and refuse are scattered throughout The Backrooms; attempts to recover or catalogue these objects are ongoing, but as yet unsuccessful. Of note are numerous graffiti resembling stick insects, various car parts, and impressive (though rudimentary) effigies of certain characters on the AI Peter stream, apparently carved out of an unknown material and painted with standard name-brand oil paints. The implications of these findings are as yet unknown, as well as who could be responsible for these artifacts.
The air within The Backrooms is thick and stifled, but tolerable and non-toxic. The temperature is uniformly warm - slightly warmer than room temperature - and the humidity is dry. Various characters report various olfactory experiences; some claim The Backrooms had no distinct scent, others claim The Backrooms had a mundane scent such as drywall, and still others claim The Backrooms had an unbearably strong odour of bodily waste.
The ambient noise perceptible within The Backrooms is an eerie silence, punctuated occasionally by the distant, muddled sounds of the AI Peter stream occurring elsewhere - like echoes of the world left behind. It is theorized for this reason by some that if one were to break through any of the nigh-impenetrable “walls” within The Backroom, they would emerge in a valid stream location somewhere.