Gamma-ray bursts (GRBs) are an amazing class of transient phenomena as their study can impact a large number of fundamental topics of astrophysics, from ultra-relativistic physics to stellar evolution, from the physics and origin of jets to galaxy evolution and chemical enrichment of the universe up to the study of the very first stars. Furthermore, GRBs, and their associated kilonovae, are the electromagnetic counterparts of the gravitational waves detections associated with neutron star mergers, and therefore they are major players in multi-messenger astrophysics. In this seminar, I will provide a review on the use of GRBs as probes, also in the context of future challenges and future facilities.