Shanghai, it's not uncommon for me to come across groups of people dancing. They gather in parks in the evenings or in front of shopping malls on the weekends to dance the waltz, the cha-cha, even the tango. I'm amazed at how many Chinese people can dance a decent mambo.
Usually there is a boom box or stereo set up outside, which plays a variety of music suitable for ballroom dancing, & anyone can join in - it's free to dance.
So far, I've just been a spectator at these events. I haven't figured out if you need to bring your own partner or if you just wait on the sidelines until someone asks you to dance, but I think it would be fun to participate in a public dance session like this. I don't know many moves, but it's just for fun anyway.