After 40 years, the Swiss firm's ideas and approaches are still fresh with each new project.

Kleinbasel is a little wedge of Basel, Switzerland, stranded in Germany, just across the Rhine from the city proper. Today the district is a hub for both commerce and culture—most famously as the home of Art Basel, the annual fair that turns the city into the capital of the global art world every June. But in the 1950s, Kleinbasel was a sleepy place, a working- and middle-class redoubt bounded to the north by woods and vineyards and to the south by the river, warm enough in summer to swim in despite the rushing current...