  The CRESST-III experiment which is dedicated to low-mass dark matter search
uses scintillating CaWO$_4$ crystals operated as cryogenic particle detectors.
Background discrimination is achieved by exploiting the scintillating light
signal of CaWO$_4$ and by a novel active detector holder presented in this
paper. In a test setup above ground, a nuclear-recoil energy threshold of
$E_{th}=(190.6\pm5.2)$eV is reached with a 24g prototype detector, which
corresponds to an estimated threshold of $\sim$50eV when being operated in the
low-noise CRESST cryostat. This is the lowest threshold reported for direct
dark matter searches. For CRESST-III phase 1, ten such detector modules were
installed in the cryostat which have the potential to improve significantly the
sensitivity to scatterings of dark matter particles with masses down to
$\sim$0.1GeV/c$^2$.
