Aqua Tower

The site is boxed in by taller neighbours, so Gang designed the balconies to reach past them. Each slab edge was drawn to give particular apartments a sightline — to the lake, to Millennium Park, down a specific street — and the results were then smoothed into a continuous topography running the full eighty-two floors. Nothing about the structure is unusual: a concrete frame, a rectangular core, flat plates. That was the economy of it, since the variation lives only in the formwork at the slab edge, and the tower was built for the cost of a conventional one. The projections do several jobs at once. They shade the glass in summer, break up the wind that would otherwise organise into a vortex against a tower this slender, and give birds a visible obstacle instead of a mirror. At 262 metres it was, when it opened in 2009, the tallest building in the world designed by a woman.