Gio Ponti + Pier Luigi Nervi's 1958 Milan skyscraper — tapered profile, hexagonal section.
From Wikipedia
Pirelli Tower is a 32-storey, 127 m (417 ft) skyscraper in Milan, Italy. The base of the building is 1,900 m2 (20,000 sq ft), with a length of 75.5 m (248 ft) and a width of 20.5 m (67 ft). The construction used approximately 30,000 m3 (1,100,000 cu ft) of concrete. The building weighs close to 70,000 t with a volume of 125,324 m3 (4,425,800 cu ft).