  We employ high-spatial resolution spectropolarimetric observations from the
Solar Optical Telescope on-board the Hinode spacecraft to investigate the fine
structure of the penumbral magnetic fields. The Stokes vector of two neutral
iron lines at 630 nm is inverted at every spatial pixel to retrieve the
depth-dependence of the magnetic field vector, line-of-sight velocity and
thermodynamic parameters. We show that the azimuthal angle of the magnetic
field vector has opposite sign on both sides above the penumbral filaments.
This is consistent with the wrapping of an inclined field around the horizontal
filaments. The wrapping effect is stronger for filaments with larger horizontal
extensions. In addition, we find that the external magnetic field can penetrate
into the intraspines, leading to non-radial magnetic fields inside them. These
findings shed some light on the controversial small-scale structure of the
sunspot penumbra.
