

Your local city college may or may not offer free classes (in San Francisco, you just need to show proof that you live in the city with some legal status).
Some public transportation is free for certain groups (youth and folks experiencing homelessness can get free passes here).
“First X of the month” at the zoo/a museum/whatever — lots of venues have free events.
A jog, bike ride, hike — lots of great stuff outside!
Good point — it is “incrementally free,” although I guess if you count tire wear and tear that’s not even true.