Here is a very partial list of sites I enjoy.
lesswrong - Becoming smarter, maybe.
slatestarcodex astralcodexten- This has become a sort of unofficial nexus for rationalist oriented people. Scott writes well.
gwern.net - Interesting reads, especially about AI/machine learning related topics. Also a weirdly large amount of content about manga and anime? I borrowed liberally from this site’s source code.
Paul Graham’s blog - He writes thoughtful essays.
Shtetl-Optimized - Scott Aaronson’s blog about computer science and quantum computing. He does a good job of, among other things, demolishing some popular misconceptions around quantum computing. He even collaborated with the people at smbc-comics to make a funny comic about the topic, which everyone should show to their children.
John Baez’s blog - It can be overwhelming to realise the breadth of learning of people like John Baez - reading blogs like this while a postgraduate student made me confront my own limited mathematical ability, which I realised is very slight and inconsequential. This realisation, combined with some pragmatic constraints, led to me deciding against a PhD in physics.
Terry Tao’s blog - As above. I am particularly fond of this post, which is helpful in making sense of certain funny looking sums.
Matt Strassler’s blog - Mostly about particle physics. I especially recommend his posts about extra dimensions and Kaluza-Klein theories: see here, here, and here.
bay12games - The dev page for dwarffortress, a game of staggering
obsession madness genius. Strike the earth!
nethack - A classic roguelike. Give it a go!
angband - Another classic, with some flavor from Tolkien’s legendarium.
caves of qud - Science fiction themed roguelike RPG, with a setting reminiscent of the Dying Earth genre.
abstrusegoose - One of my favorites - underrated and sadly not updated for some time (as of early 2021). I particularly like this one.
xkcd - Classic science/tech/nerd comics.
oglaf - Dirty jokes, NSFW.
existential comics - Informative and titillating philosophy jokes.