Visitors to Market Square Park can pause on their stroll through the downtown centerpiece for a palpable experience of its past. Houston's first four city halls laid their foundations here, and relics of the square's heritage remain embedded in the sidewalks of the park. Chalk up a chance sneeze on Milam Street to the final ghostly gasp of dust from Robert Boyce's sawpits. Step from Congress Street into La Carafe, Houston's oldest commercial building,...