Becoming a dancer opened up all sorts of doors for me. It made me comfortable in social situations from small-talk in intimate groups to public speaking in front of large ones.
I even ended up married and living in a foreign country. Currently I'm learning the language and making some progress. All of which I can trace fairly directly to learning to dance.
Caveats:
You need to like the music! So pick a form that's compatible with that (if there is one).
Don't go into this looking for a hook-up. Those people are greatly disliked by most of the people in the scene.
Obviously this is open to confident people too, but shy people will likely get more out of it because the structured nature of dance classes compensates for lack of confidence.
(Also, for all the "two left feet" people - if you can clap a rhythm to a song, you can learn to dance just fine)