Just finished the latest Lee Child (Jack Reacher) book,

titled 'Make Me', that was about the Dark Web or Deep Web. Good analogies include the conventional internet is like an iceberg, with the Dark Web being the part below the surface. Legitimate sites, that can be found on Google, are like tennis balls, with glue and spikes on them, so they can be detected. The dark web sites are like smooth, oiled, polished marbles, that can't be detected/picked up, unless you know a 'specific' address, and cross several firewalls, that continually move and change. Good article in the new 'Rolling Stone' mag, about how they work, as international drugs, arms, smuggling, hackers and hacker's info, pedophiles, Republican strategists, human trafficing, etc, sites exist and prosper. Kinda scary, but interesting, as bitcoins become more common and the accepted currency of the darknet.
If I was a criminal, I'd check out Torproject.org/ configuring hidden services