10 things to do at the park
1. Designate a small area and declare your own micronation
2. Have some cold drinks
3. People watching
4. Pigeon watching
Or squirrel watching! Or rabbit watching! Depending on the park.
5. Play mölkky
I used to play this back in 2016 or so. Some sort of Finnish bowling in which you throw a stick.
6. Make friends
7. Read a book
8. Sleep there at night
Safety will depend on the park and on the city. Often not allowed. If it's a gated park that closes at night and you manage to trespass (which is obviously illegal), you might not have anybody else around.