Some surfing of Euro sites for "rabbit warrens" may inspire you. The European's tend to have smaller living quarters and really pack it in, although most is on smaller gauge layouts.
I have 6 tiny layouts using 0-27. 2 are hand bent down to 0-21&o-19. None measures more than 31" anywhere. 3 are on one 30x30" table (around bottom of legs, & one halfway up, & one on the top. (plus a 4.5x9, + a ceiling loop...and more )
I'm ready for a nursing home train wise