Gamma-Ray Bursts are brief flashes of gamma-rays on the sky, and they produce so-called afterglow emission, from X-ray to radio, which lasts for days to weeks. While many details of the origin of the burst and afterglow emission are still open, the afterglow emission can be used as beacon to probe the distant Universe. I will report on both, an instrument (GROND) specifically developed for ground-based afterglow observations, and some results obtained since its commissioning in 2007: (i) chasing high-redshift bursts, (ii) determining the origin of dark bursts, (iii) investigating
the surprising wealth of light curve variability.
