[apologies, wall of text follows] A number of other people have suggested sports. I wish I had discovered Judo and Brazilian Jujitsu younger, but I was a compe

[apologies, wall of text follows] A number of other people have suggested sports. I wish I had discovered Judo and Brazilian Jujitsu younger, but I was a competitive fencer and boxed in university. All sports give you a pool of people to have shared experiences with (maybe a bit artificial) whether they are team sports or individual sports. The other element of these kind of 'instant friend' activities is that you can find a kind of 'placeholder' group of people to hang out with who may be able to introduce you to other people you are more likely to click with. I made some good friends from groups of people that I largely had nothing in common with but was hanging out with because of some girl (for example) - but you might wind up meeting way more interesting people on the periphery of a group you don't really 100% click with. My friends in high school were generally 'shared interest' nerd friends (mostly Dungeons and Dragons as a core nerdy interest). It's possible to make friends doing pretty much whatever - a lot of friends I had in university were my peers in CS and other subjects. We had to hang around in labs and classes together, though (and having a 4th year "honours" program in CS where we did 100% CS and all had on-campus shared offices was really good for that). So it's just as possible that you could wind up walking in, doing your work, and walking out. Cultivating some projects and working with a group might really help with that. A lot of undergraduates are considered disposable randos who are just interested in getting a qualification as quick as possible while accumulating as little extra knowledge as possible, but if you're interested in type theory, maybe you should be trying to work with a research group in something you like. Ideally go for a healthy research group that's actually at the place you want to go, not something that exactly fits your supposed interested right now (which will likely change). So if they have a big healthy machine learning group that welcomes undergraduate research interns vs one cranky weirdo doing type theory, do the former (that's better both socially and, likely, as research prep if that's the direction you want to go). Do try to make sure that you're not assuming activities are asocial when they aren't, too. Maybe people are getting coffee after art class? It's very hard to force the issue - I think people are more and more preoccupied with their phones and previous social connections via social media than they are interested in meeting new people. I suggest cultivating a lot of interests (including a wide variety of things), behaving yourself well, keeping an open mind and seeing what happens. Of course, maybe you're just solitary by nature. But don't assume stuff. I substantially reinvented myself in university and essentially declared myself an extrovert after having been very introverted in HS. Despite some awkward moments from this forced transition (yes, someone trying to put on an extrovert skin can be about as dreadful as you might imagine) this was a very good idea long-term.