Graphically it should suggest the experience of wandering the stacks of a large library. Have you been in the stacks of a big University or city library? Narrow, ill-lit aisles, books shelved on both sides, from the floor to well above your head. Oooh! Oooh! you could model it after Terry Pratchett's Unseen University Library[1].
be forewarned that the reason it's asking you to use only #'s and spaces is the effect only works if the ascii image is very contrast-y. if the ascii art makes use of gradients (....:::;;;iiii@@@@) the effect won't be as obvious or work at all.