  Over the last decade there has been immense progress in the follow-up of
short and long GRBs, resulting in a significant rise in the detection rate of
X-ray and optical afterglows, in the determination of GRB redshifts, and of the
identification of the underlying host galaxies. Nevertheless, our theoretical
understanding on the progenitors and central engines powering these vast
explosions is lagging behind, and a newly identified class of `ultra-long' GRBs
has fuelled speculation on the existence of a new channel of GRB formation. In
this paper we present high signal-to-noise X-shooter observations of the host
galaxy of GRB130925A, which is the fourth unambiguously identified ultra-long
GRB, with prompt gamma-ray emission detected for ~20ks. The GRB line of sight
was close to the host galaxy nucleus, and our spectroscopic observations cover
both this region along the bulge/disk of the galaxy, in addition to a bright
star-forming region within the outskirts of the galaxy. From our broad
wavelength coverage we obtain accurate metallicity and dust-extinction
measurements at both the galaxy nucleus, and an outer star-forming region, and
measure a super-solar metallicity at both locations, placing this galaxy within
the 10-20% most metal-rich GRB host galaxies. Such a high metal enrichment has
implications on the progenitor models of both long and ultra-long GRBs,
although the edge-on orientation of the host galaxy does not allow us to rule
out a large metallicity variation along our line of sight. The spatially
resolved spectroscopic data presented in this paper offer important insight
into variations in the metal and dust abundance within GRB host galaxies. They
also illustrate the need for IFU observations on a larger sample of GRB host
galaxies at varies metallicities to provide a more quantitative view on the
relation between the GRB circumburst and the galaxy-whole properties.
