One of the most interesting examples of symbolism to my mind in this excellent short story is the way in which the physical description of Dr. Jekyll's house and laboratory mirrors the internal division between himself and Mr. Hyde and exemplifies the dual identity that he has. Note how the house of Dr. Jekyll is described as being very elegant and comfortable. Note the description of the hall we are given as Mr. Utterson is ushered into Dr. Jekyll's house for the first time:
...a large, low-roofed, comfortable hall, paved with flags, warmed (after the fashion of a country house) by a bright, open fire, and furnished with costly cabinets of oak.
Utterson himself regards this room as the "pleasantest... in London." This of course is a symbol of the debonair and socially respectable Dr. Jekyll. Yet the laboratory that lies at the rear of Dr. Jekyll's abode is described in very different terms, as a "certain sinister block of building." Its signs of decay and neglect clearly link to the character of Mr. Hyde and his perversity and evil. Note, too, that both sections of the house overlook different parts of London, so that you would never know that the two sections were actually linked from outside, just as in the same way that you would never imagine that there could be a relationship between Dr. Jekyll and Mr. Hyde is you looked at them.
You could also say about the size and looks of Hyde.
He was significantly smaller than Jekyll and uglier, suggesting that in every person, the amount of badness within them, is smaller (Hyde) than the amount of goodness (Jekyll)!!!!