Hi! I'm an American expat, living in Göteborg for a bit over a year now. My partner's 30th birthday is this year, so I've spent quite a bit of time trying to find something unique and fun to do for him. (He's lived in Göteborg his whole life and has already done all of the "regular" activities.) What I ended up doing was booking an event through the companies I work for, Mondiala Entertainment and Eventligan. This worked out really well! He loved doing something unexpected (being in the woods at night in the middle of a "zombie apocalypse"), and it was great that all of his friends could do it with us. I really recommend that - if you also are looking for something a bit out of the ordinary, whether it's shooting guns, competing at trivia, or killing zombies - you give it a look: eventligan.se and mondiala.se.
I'd love to hear about other fun events and activities people have found, so that I can start planning for next year!