Meanwhile, Alice is combing the area invisibly, looking for a good place to put his magic door. Preferably near Bella's building; ideally in Bella's building.

[Ooh,] he says musingly over brainphone. [How about the bottom of the stairs?]

Not that many people take the stairs in a building with elevators anyway, and the ones who do probably don't head down to the basement that often. The space under the last turn of the stairs is plenty wide enough for a magic door; hell, it's wide enough for two.