Tianzifang is partly known for this architecture, which I had to look up to find the name...shikumen. Between these 2-3 story structures are narrow alleys, along which are galleries and shops, some selling communist kitsch, others selling stationery with mangled English. The narrow alleys are hellish on a Saturday afternoon, but I've braved them more than once.
Another favorite was the place that sold ocarinas. In a former life I was a flutist, and I own more than a couple of these clay whistles. It was incredible to see them in so many shapes and sizes.