"The cave you fear to enter holds the treasure you seek." -Joseph Campbell
Space, as you know, is mostly empty, as the typical distance between galaxies far exceeds the size of the galaxies themselves.
But in a few select regions of the Universe, where the mass density is unusually above average, galaxies cluster together by the thousands. The closest huge cluster to us like this is the Coma Cluster, containing more galaxies than 95% of all known galaxy clusters.