Reddit is awesome and fully deserving of its tagline as "the front page of the Internet". A great place to find quality content, or to discuss literally anything under the sun.
Some of my favourite and most visited subs:
r/AskReddit – I always read this on my train journeys home after a long day at work. Often has really weird, unique and/or interesting discussions
r/CatastrophicFailure – this can be a little disturbing and NSFL, but contains really interesting and dramatic footage of accidents
r/CozyPlaces – pictures of small, warm, calming places
r/Futurology – best place for all the latest tech, although it seems a little obsessed with climate/environment issues
r/HybridAnimals – hilarious pics of animals "combined" with other animals in Photoshop
r/introvert – a great place to relate to other introverts (although I think I'm more of an ambivert, these days)
r/LateStageCapitalism – if you ever want to rant against capitalism, this is the place for you
r/london – a sub for my home town. I'm sure Reddit has other subs for just about every city and country on earth
r/MediaSynthesis – a great sub, created by Yuli, covering the latest advancements in AI-generated and manipulated content
r/MovieDetails – very interesting observations of little details you might have missed in movies
r/nottheonion – real-life news stories that are so absurd or bizarre, they could be mistaken for satire
r/politics – political news and discussions
r/science – all the latest science, often discussed by experts/professors whose comments get upvoted to the top, so it's really interesting to get their perspective on developments
r/technology – ditto, but for technology
r/thalassophobia – creepy/dark pictures of underwater scenes, both real and imaginary
r/TheDepthsBelow – very similar to r/thalassophobia, but with more focus on the real world, sea life, etc.
r/TrueReddit – a really high-quality sub with intelligent, mature discussions about news and social issues. No clickbait here.
r/unitedkingdom – the place I go to rant about Brexit and everything else UK-related
r/WeatherGifs – self-explanatory
r/Whatcouldgowrong – hilarious, but also quite disturbing videos of people doing stupid things
r/worldnews – similar to r/politics, but with more "general" news