For me, it's social dancing, specifically West Coast Swing. Because while there is just social dancing, and some who only do it, there's a bit of a culture of competition, and it has its own governing body for determining where you place in competitions, and when it does sound like a cult when described.
Oh my god, I've been thinking about this on and off since weeks. I need to make playlists for my friends showcasing stuff they would like. But there's so much to choose from!