Square, hollow section steel with a slender, 20 mm cross-section gives form to the thirteenth Serpentine Gallery Pavilion; the bars are positioned on a 40 cm grid to create an open structure (surface area: 357 m2) that can be entered. In the event space (floor area: 142 m2), a mobile cafétheque and glazed seating steps invite ­visitors to stop and linger. The structure was pre-fabricated in a factory in York in 50 transportable modules. In ­London these were connected via push-in sleeves, then field-welded. To provide protection from the rain, the design of the roof stipulated the use of transparent, shingle-like, overlapping plastic shingles. (Frank Kaltenbach conducted the interview with Sou ­Fujimoto on April 4 at the VitraTalks in Weil am Rhein, and on June 8 at the opening of the Serpentine Gallery Pavilion in London.)