Cheap/free things to do for my birthday?

Hi everyone! So, today's my birthday (level 38!) and im looking for something to do today or this weekend. I live paycheck to paycheck, so I don't have a lot of extra money, but if anyone has ideas I'd love to hear them!

I live right by forest park, and go to the zoo, science center, and art museum fairly often, so im hoping for something new/different, and preferably something I can do by myself, since I'm pretty introverted.

Also, if anyone knows of places that do birthday freebies, that would be awesome as well!

Thank you in advance!