On an unrelated note, many people dont realise that Ye Olde cities you often see in Europe (the medieval areas separate from the 18th/ 19th century 'New Towns') only survived because they were such undesirable areas to developers over the ages. Communal loving very much the name of the game, and buildings actually designed for multiple families rather than the one.
London's notorious East End and Southwark, if they hadn't been bombed flat in the war may well have ended up being touristy Old Towns:
George Inn, once one of the most notorious alleys, now a celebrated pub
3 Worst slum's in London - Devil's Acre and Jacob's Island:
Notting Hill's Potteries and Piggeries - note what could become shop fronts and basement levels