You've heard about the dark web - that deep undercover element which is full of illegal offerings, which has until now been really difficult to search. You needed to download and use the TOR browser which provides reasonable anonymity, and then hunt down the content that you're looking for. Well, there's a new resource available which is actually indexing pages and making them available as regular .html content. Because it's doing that, Google can now index them itself. Currently there's only about 650,000 pages, but I think you can rest assured that there will be more in the future. Simply get thee hence to Onion City and try it out. You'll actually find that you're searching a Google custom search engine, so if you prefer, you can go direct to Google and run a site search on site:onion.city for the same results.
Why would you want to find illegal, nefarious information? I have no real idea, but you might want to do it so that you know what's out there, how easy it is to find it, and what other people are doing. You may also be required to find out how much a fake passport costs, or if amphetamines are available online and if so, what they are.
You can simply go to the site and type in your search term(s):
Alternatively, simply go to Google and do a search for your search term(s) and add in site:onion.city and you'll get pretty much the same result.