The Fenchurch Building in the City of London, commonly known as the “Walkie Talkie”, gained notoriety shortly after it opened when it was discovered that its concave facade acted as a parabolic mirror and could melt cars parked beneath it if the sun was shining from the right direction. Since then, apparently, the windows have been treated to prevent such destructive events.
In this view, the building can be seen with part of Southwark Bridge and Cannon Street Station in the foreground.
For the technically inclined...