Off the top of my head, here are a few fun sites!
Pretty well known, but there’s always Flightrising, a virtual pet sim with dragons that you can design, dress up, breed, and more! Has a very active userbase and a lot of different mechanics and playstyles you can focus on. You don’t need an account to look at a lot of flightrising stuff, so it’s easy to check out what it’s about!
Another popular site, there’s SCPwiki where you can read a lot of cool horror/sci fi stories about supernatural items and entities being contained (or not contained) by a questionable organization. The site is a huge collaborative and creative effort by tons of different people, and it’s easy to spend a ton of time reading entries.
And for more niche sites:
Mushroomexpert is literally one retired English teacher who was created probably the most in depth and comprehensive guide to mushrooms that grow in America out there. He’s spent decades finding and characterizing different mushroom species and writing extensive and often numerous notes on each, and pretty much every mycological site out there cites him because he’s done so much. He also has a ton of dichotomous keys and various guides if you ever want to identify a mushroom.
Nautilus Live livestreams ocean exploration by the Nautilus research vessel, including remote control vehicle deep sea exploration. Since it’s a livestream it isn’t always online or doing much (for example at night or when the ship is in port) but when it is it’s really fun to just put on in another window and listen, you get to hear scientists talk live about things they find in the deep ocean, and sometimes they slurp up things with a big tube. Though when it’s offline you can always look at stream highlights too.
