  The boundary layer flow in a Rayleigh-B\'enard convection cell of rectangular
shape has been visualized in this fluid dynamics video. The experiment has been
undertaken in air at a Rayleigh number $Ra=1.3\times 10^{10}$ and a Prandtl
number $Pr=0.7$. Various sequences captured at selected positions of the
heating plate show that the boundary layer is a very transient flow region
characterized by coherent structures that permanently evolve. It becomes fully
turbulent in the areas where the large-scale circulation impinge or leave the
bottom plate.
