Radio ghosts are phenomena of extended radio emission which are frequently found within or at the periphery of large-scale structures of the universe, preferentially in galaxy clusters.
Their origin is still unknown both for the extended ghosts (called radio halos) and for the more concentrated ones (called radio relics, phoenixes, or plumes).
A natural scenario for their origin is (re-)acceleration of relativistic electrons by intra-cluster plasma shocks, but the various attempts to use this baryonic physics revealed many inconsistencies and problems.
A more exotic scenario is provided by the annihilation and/or decay of dark matter particles dominating the gravitational potential wells of galaxy clusters; this model provides the attractive possibility to use radio ghosts as portals to explore the dark universe and in particular the nature of dark matter in the universe.
I will discuss the current and future strategies to use radio ghosts as portals to the dark universe or probes of new baryonic physics in the large scale structures of the universe.