http://redlib.nowhevi57f4lxxd6db43miewcsgtovakbh6v5f52ci7csc2yjzy5rnid.onion/r/hacking
Through CTF you learn literally everything there is about the digital world, in a rather intense but exciting way. Almost all the creators/finders of major exploits have dabbled in CTF in some way/form, and almost all of them have helped solve real-world issues.