  Dark Matter (DM) is an elusive form of matter which has been postulated to
explain astronomical observations through its gravitational effects on stars
and galaxies, gravitational lensing of light around these, and through its
imprint on the Cosmic Microwave Background (CMB). This indirect evidence
implies that DM accounts for as much as 84.5% of all matter in our Universe,
yet it has so far evaded all attempts at direct detection, leaving such
confirmation and the consequent discovery of its nature as one of the biggest
challenges in modern physics. Here we present a novel form of low-mass DM
$\chi$ that would have been missed by all experiments so far. While its large
interaction strength might at first seem unlikely, neither constraints from
particle physics nor cosmological/astronomical observations are sufficient to
rule out this type of DM, and it motivates our proposal for direct detection by
optomechanics technology which should soon be within reach, namely, through the
precise position measurement of a levitated mesoscopic particle which will be
perturbed by elastic collisions with $\chi$ particles. We show that a recently
proposed nanoparticle matter-wave interferometer, originally conceived for
tests of the quantum superposition principle, is sensitive to these collisions,
too.
