  The inner 20 gravitational radii around the black hole at the centre of
luminous Active Galactic Nuclei and stellar mass Black Hole Binaries are now
being routinely mapped by X-ray spectral-timing techniques. Spectral blurring
and reverberation of the reflection spectrum are key tools in this work. In the
most extreme AGN cases with high black hole spin, when the source appears in a
low state, observations probe the region within 1 gravitational radius of the
event horizon. The location, size and operation of the corona, which generates
the power-law X-ray continuum, are also being revealed.
