The SCP foundation has been mentioned, but a lot of people don't know they have a sister site. http://wanderers-library.wikidot.com
The wikipedia articles about unsolved problems in physics and emerging technologies are huge click holes for most nerds:
https://en.wikipedia.org/wiki/List_of_emerging_technologies
https://en.wikipedia.org/wiki/List_of_unsolved_problems_in_p...
Reading about neolithic archaeology is way more fun than you might think. 10,000 years ago people built these huge sites with literally stone age technology, and the nature of their rituals and beliefs are mostly unknown.
https://en.wikipedia.org/wiki/Neolithic#Early_settlements
Shodan is a search engine for devices on the Internet. Looking at other people's queries is a good way to get started. Every time you think, there's no way someone would connect one of those to the Internet, you find out that at least 10 people have gone and done just that. https://www.shodan.io/explore
Running an NTP server in the public pool gives you the IPv6 addresses of all kinds of whacko IoT stuff. Every once in a while p0f can't figure out a TCP/IP stack that's connecting to my server, so I connect back and there's sometimes a really weird device with an open telnet or HTTP port or something. About once a month I have to call someone to tell them that they misconfigured their firewall when they turned on NTP and I'm logged into an air conditioner on a cruise ship or another bizarre combination of thing and place that I never thought I'd ever say out loud. Browsing the logs is a never-ending source of amazement.
PSA: connecting to public NTP servers exposes you to people like me, don't do it unless you have to.