Dark Manhattan
An alternate universe dominated by the Lone Power, where Nita, Kit and Fred find themselves trapped during the events of SYWTBAW.
From the phone conversation that the three of them overhear while hiding in the Lone One's office building, this universe is apparently one to which the Lone One was exiled after Its defeat in the Cosmomachy. The Lone Power complains bitterly to the person on the other end of the phone -- almost certainly the Michael Power, since the Lone One calls him "Mike" -- about the low energy levels inherent in the space, where there is no power to spare even for light almost anywhere except in Its own HQ. It also voices Its fury at what It considers the purposeful interference of the Powers that Be on what It has come to consider Its turf. Nita and Kit, already seriously upset by (as they initially see it) having been tricked into this gloomy, scary place and then pursued through the dark empty streets by packs of the Lone One's perytons, are by this point mostly intent on getting away from the Lone Power and back to their own Manhattan as soon as possible -- not yet realizing that in this, they're only going to be partially successful.
Tales of pocket dimensions or closed-curve universes in which various forms of the Lone Power are confined are a commonplace among the billions of inhabited worlds across the Galaxy. These spaces are usually referred to as phulakic volumes. (The Greek root-word for prison is here used as a nod toward the much more precise and specific Speech-word, aiyutheneitamal, which indicates an enforced confinement secondary to a judicial proceeding.) It's interesting to note that, in this connection, various philosophical and religious texts on Earth and elsewhere speak of "the spirits in prison" -- a phrase having nothing to do with deceased mortal beings -- who are "bound in darkness". (Entirely incidentally, some of these texts also mention the concept that these imprisoned spirits are worth interceding for with the One... the idea being that the imprisoned wrongdoers might eventually be redeemable.) The darkness in question is apparently the same low-energy state which is reported of the dark Manhattan, the other Powers' intention apparently being to give the Lone One as little raw material as possible with which to work Its inevitable further mischief.*
Nonetheless, the Lone Power's cruelty will usually find a way to make do with whatever little power and matter are available, with the goal of marring whatever works or mocking the One's intentions. By the time Kit and Nita have arrived, the Lone One has turned the dark Manhattan into a place of energy-starved metalife, prowling predatory machines, and horrific constructs bent on destroying whatever genuine life might actually stray into the place. There is no Sun in this universe, and there are no stars -- a situation which causes Fred considerable distress. The lack of astronomical bodies raises questions about the actual extent of this universe: whether it has a size similar to our own universe's, and merely lacks enough energy to have stars in the first place: or whether it's a much smaller closed volume. This question would of course have to be resolved by an actual survey... a project which most wizards would be forgiven for not being terribly interested in undertaking. But the low-energy thesis may have some value, considering that the Lone Power went to some trouble to have the Book of Night with Moon stolen and brought into Its world of confinement. There Its power, uncontested by other energy sources, would be able to damp down the Book's virtue sufficiently to keep it from being detected by those who were desperately searching for it.
Uncertainties remain as to why this particular pocket universe should manifest itself in the form of an alternate Manhattan at all. There may be something to the theory suggesting that phulakic volumes aren't plural, but actually singular: that all the prisons are local aspects or restatements of a single greater conditional event-space that interpenetrates countless other less senior dimensions and planes in the same the way that Timeheart does. If this theory is accurate, then wizards who make their way into a phulakic volume may themselves to some extent be responsible for the way it looks. The mere introduction of the extra energy of their transit and presence into such a previous volume, and the power of their living minds, may help to shape the inner appearance of the restricted volume into something the visiting wizard is better equipped to cope with or alter. (SYWTBAW)