Some ideas found on Ask Reddit
1. Join an adult sports recreational team.
2. Volunteer at an animal rescue shelter.
3. Learn a musical instrument.
4. Go to a museum (look online to see which are free or if there are any reduced price days to visit)
5. Take up a physical activity, like rock climbing, swimming, or hiking.
6. Look online for game nights in your area (like trivia night, board game night, etc.)
7. Learn a new language (or brush up on an old one)
8. Take up Geocaching
9. Start going to the library more regularly (and take advantage of all their resources, like movies and video games)
10. Explore nearby towns/suburbs and see if you can find a cool new place you’ve never been to before (like a cafe or gallery)
11. If you live in a town with a subway or metro, ride it around the city to check out the graffiti and people watch
13. Take up writing, whether that means journaling or creating a new project
15. Watch YouTube tutorials to learn a new skill
16. Sign up for online classes and spend a certain amount of time per day learning something new
17. Put paper on your wall, get some bargain bin paints from Walmart, and go crazy
18. Take up yoga
19. Take up gardening and watch your hard work flourish
20. Get in touch with your inner child and try getting back into some of your childhood hobbies, collecting Pokemon cards or coloring for no reason
21. Spend time learning how to cook new dishes or experimenting with tweaking old ones
22. Check out the cultural/community events in your city
23. Look for online communities or threads full of people who are interested in the same things you are (i.e. TV shows you like, video games you play, sports teams you follow, etc.)
24. Look for free/cheap concerts and stand up comedy shows nearby
25. Volunteer for organizations you’re passionate about and meet like-minded people (as well as build your resume)