  We present results of numerical 3D MHD simulations with radiative energy
transfer of fine structure in a small sunspot of about 4 Mm width. The
simulations show the development of filamentary structures and flow patterns
that are, except for the lengths of the filaments, very similar to those
observed. The filamentary structures consist of gaps with reduced field
strength relative to their surroundings. Calculated synthetic images show dark
cores like those seen in the observations; the dark cores are the result of a
locally elevated $\tau=1$ surface. The magnetic field in these cores is weaker
and more horizontal than for adjacent brighter structures, and the core support
a systematic outflow. Movies show migration of the dark-cored structures
towards the umbra, and fragments of magnetic flux that are carried away from
the spot by a large scale `moat flow'. We conclude that the simulations are in
qualitative agreement with observed penumbra filamentary structures, Evershed
flows and moving magnetic features.
