Figure (a) shows the complex turbulent velocity field near a heated horizontal surface obtained by particle image velocimetry. This random velocity field contains organised motion of coherent structures, which could be extracted from the velocity field as shown in figure (b). The coherent structures, shown as blue lines in the view from above in figure (b), are rising sheets of fluid that transport the heat away from the surface. The red arrows show the cold fluid impinging on to the hot surface in between these structures. The rising sheets move around laterally and merge, with new sheets being formed in the vacant regions. Understanding these complex dynamics is essential whereever turbulent heat transfer from horizontal surfaces occur; the applications range from heating a pale of water to our climate.