Gehörgang: 
yes, people walk through it. 
inside walls are covered with sound absorbant materials.
therefore the sounds (from outside) are muted.

certainly the piece makes more sense when it is NOT situated in an absolute silent place but in a vicinity where there is at least SOME noise.

i have no experience with polystyrene. i dont know if the acoustic effect is right with that. but maybe. 

in the swiss version the outside walls and the roof where from OSB (wood) panels 15mm (bold black in the sketch "Grundriss.gif"). while the sound absorbant material (white outlined in the sketch) where soft (!) matts of 100mm wood wool (Holzwolle, excelsior). and in order to not get in touch with the matts they were covered with thin "drainage foil" (Drainagefolie)

"wood wool" is the material a carpenter would use for the inside insulation of the roof of a house. not for acoustic insulation, but for thermal insulation! this material acoustically works better than everything else i know - and it is cheap!

i hope also that "drainage foil" is the right translation. but it could be thin (!) cotton as well.