A very fun NPC I've had in one of my games. His whole deal is that he acts very stoic and suspicious, mysteriously wandering off into the snowy wilderness every day. His coworkers at the tavern he works at have no idea where he goes or what he does every day. As a sidequest I have one of his coworkers ask them to figure out if he has a secret significant other or something. Instead they find out that he's doing Ice Dance Practice, usually to songs by ABBA. He's also REALLY good at it. He keeps it secret because his goliath clan banished him for having such "frivolous" and "embarrassing" interests.