The important thing to remember here is the fact that the sites Google indexes represent only about 4% of websites in the entire world. This is the “visible” web. The rest is considered the deep web, or even the dark web. These are sites that are intentionally hidden for NUMEROUS reasons. It contains political dissident material, cp, drugs, guns, etc. In order to access these… you will need Tor. Although… I don’t really recommend messing around with the Deep Web unless you have a compelling reason to.
Edit: Deep web is estimated to be about 7 zettabytes in size… which is massive.