  The spectral window, containing Fraunhofer lines formed in the solar
photosphere, around the magnetically sensitive Cr I lines at 5780.9, 5781.1,
5781.7, 5783.0, and 5783.8 \r{A}, with Land\'e g-factors between 1.6 and 2.5,
is explored. The goal is to analyze simultaneously 15 spectral lines, which
comprise Cr I, Cu I, Fe I, Mn I, and Si I lines, without polarimetry to infer
the thermodynamic and magnetic properties in strongly magnetized plasmas using
an inversion code. The study is based on a new setup at the Vacuum Tower
Telescope (VTT, Tenerife) which includes fast spectroscopic scans in the
wavelength range around the Cr I 5781.75 \r{A} line. The snapshot 385 of the
Enhanced Network simulation from the Bifrost code serves to synthesize all the
lines, which are in turn inverted simultaneously with SIR to establish the best
inversion strategy. This strategy is then applied to VTT observations of a
sunspot belonging to NOAA 12723 on 2018 September 30 and the results are
compared to full-disk vector-field data obtained with the Helioseismic and
Magnetic Imager (HMI). The 15 simultaneously inverted intensity profiles
(Stokes I) delivered accurate temperatures and Doppler velocities when compared
against the simulations. The derived magnetic fields and inclinations are most
accurate when the fields are oriented along the line-of-sight (LOS) and less
accurate when the fields are transverse to the LOS. In general, the results
appear similar to the HMI vector-field data, although some discrepancies exist.
The analyzed spectral range has the potential to deliver thermal, dynamic, and
magnetic information in strongly magnetized features on the Sun, such as pores
and sunspots, even without polarimetry. The highest sensitivity of the lines is
found in the lower photosphere, on average around $\log \tau = -1$. The
multiple-line inversions provide smooth results across the whole field-of-view.
