  Cosmic voids, the less dense patches of the Universe, are promising
laboratories to extract cosmological information. Thanks to their unique low
density character, voids are extremely sensitive to diffuse components such as
neutrinos and dark energy, and represent ideal environments to study
modifications of gravity, where the effects of such modifications are expected
to be more prominent. Robust void-related observables, including for example
redshift-space distortions (RSD) and weak lensing around voids, are a promising
way to chase and test new physics. Cosmological analysis of the large-scale
structure of the Universe predominantly relies on the high density regions.
Current and upcoming surveys are designed to optimize the extraction of
cosmological information from these zones, but leave voids under-exploited. A
dense, large area spectroscopic survey with imaging capabilities is ideal to
exploit the power of voids fully. Besides helping illuminate the nature of dark
energy, modified gravity, and neutrinos, this survey will give access to a
detailed map of under-dense regions, providing an unprecedented opportunity to
observe and study a so far under-explored galaxy population.
