BRIGHT lights, BIG city: Massive galaxies, giant Ly-a nebulae, and proto--clusters

High redshift radio galaxies are great cosmological tools for pinpointing the most massive objects in the early Universe: massive forming galaxies, active super–massive black holes and proto–clusters. We report on deep narrow–band imaging and spectroscopic observations of several z > 2 radio galaxy fields to investigate the nature of giant Ly-alpha nebulae centered on the galaxies and to search for over–dense regions around them. We discuss the possible implications for our understanding of the formation and evolution of massive galaxies and galaxy clusters.