At $830 per square foot, this LEED-Gold office tower designed by Helmut Jahn is the second most expensive piece of commercial real estate ever to be sold in Washington DC. Located at 1999 K Street, the building may seem underwhelming at a distance. However the uniquely expressed curtain wall is a cleanly detailed system that delivers a completely original experience. Each curtain panel is buttressed by a vertical fin of glass projecting from the flat surface of the building. The functional directive of the fins is to provide wind-load support, but their sculptural quality is what makes them so exciting. From a vantage point on the adjacent sidewalk, the fins create a mosaic effect of angular geometric transparency. The result is very subtle, and likely missed by the majority of passers by. But it is exactly this understated simplicity that leads to a profoundly graceful power. The close-up photos of the wall are worth clicking on. The lobby at night is also a vivid space.