The large majority of our Universe is dark, its vast expanse only sparsely permeated by a thinweb of matter. Inside this web, gravity has worked to form islands of light made up of immensecollections of stars. These conglomerations of matter, what we have come to know as galaxies,carry with them the story of the life they have experienced in the form of their chemical compositions.At any time, this composition is set by the seed gas from which they were formed, but alsothe inevitable enrichment carried by the stellar appetite for turning light elements heavier. Thecataclysmic explosions that either mark the end of stellar lives or are the results of mergers ofstellar remnants, scatter enriched material throughout galaxies in which they live, providing thesustenance of a new generation of stars, richer and more complex in their compositions. In orderfor us to understand our place as humans in this universe, we need to investigate the cosmichistory carried by the elements from which we are formed. This thesis investigates the mostpowerful explosions in the universe, gamma-ray bursts, how these can be used to probe the darkuniverse intersected by their light, and what consequence these events have for the universethat harbors them. I here present a homogeneously selected sample of gamma-ray burst (GRB)afterglows that are the results of more than eight years of sustained eort. This dataset is a uniqueresource that can be used to harvest the potential of GRB afterglows in illuminating the universe.These spectra contain rich information about the gas, dust, metals, molecules surrounding theGRB explosions, spanning a wide range of redshifts, thus providing unique insights in the starformation and chemical history of the universe. This treasure trove allowed me to discoverespecially signicant events and in particular, I was able to single out GRB 111117A as the mostdistant short GRB ever discovered. The study of this single event allowed to me to constrainthe intrinsic redshift distribution of short GRBs and the conditions of the progenitor system ofshort GRBs. I also present the observations of an electromagnetic counterpart to a simultaneousgravitational wave signal and short GRB, which is caused by the merger of two neutron stars.These data hold the secret to understanding the physical mechanisms behind this enigmaticphenomenon that has now come to be named a kilonova. Lastly, in these spectroscopic data ofthe kilonova, the spectral signatures of light r-process elements are identied, providing the rstcompelling evidence for the site of at least the light r-process elements.