There is very little direct characterization of Finsterwald’s in this book. Direct characterization is when the narrator of the book explicitly tells the reader things about a character or, in this case, a place. This is in contrast to indirect characterization, where readers learn things from what other characters say or think or do.
The main direct characterization of Finsterwald’s in the book comes in Chapter 36. This is found in the episode where Maniac is going to spend ten minutes in the Finsterwald’s back yard on a bet. If he manages it, Russell and Piper have to go to school for a whole week.
Maniac, Russell, Piper, and a bunch of other kids go to Finsterwald’s. This is when we get direct characterization. Maniac goes up to the house. There (p. 139 in the edition of the book that I have), we are told that the house is red brick, that it is three stories high, that it has “bile-green window shades” and a white door that has three cement steps that lead up to it.
That is the most direct characterization of Finsterwald’s to be found in Maniac Magee.