What are some cheap/free social activities and hobbies?

To build a social circle and be a more fully realized man one apparantly needs to have social hobbies and do social activities. Be among other people and have some common thing to do and or talk about.

Yoga and dancing are mentioned a lot. Teamsport is mentioned.

What else is there to do? What are cheap and or free activities / hobbies? How to find stuff like this?