Physical cosmology is my favorite bundle of pages to dive into on wikipedia; the articles are so dense with math that I don’t understand and theories that are so weird and out-there. It reminds me that I don’t know everything, and that there is so so much to know and learn about and so much more out there that has yet to be discovered.
Some highlights for me are The Ultimate Fate of the Universe, which is about theories on how the universe will end, and the Shape of the Universe, which seems like a silly thing to question but is actually a really complicated topic. It makes you think about geometry and space in a different way, and kind of breaks your brain a little bit.