If you haven't been yet, check out the Spielzeugmuseum
on Karlstraße 13. Even without kids, it's a lot of fun. Toys from the Dark Ages, toys from your childhood.... Dolls, trains, Legos, building sets, rockets, hobby horses.... I enjoy seeing what passed for fun in other times!
Take in a football game for the experience if you have not been before.
Or the Ice Tigers -- a couple weeks left in their season. Lots of fun!
Stay on the U-bahn after the last stop, then let me know what happened and how long it was until you could get off. Always wondered.
Did this once... about 4 of us ended up missing the last U11 stop at Eberhardshof. It pulled off the tracks and sat in between for about 10 minutes (as a short train) then back to Eberhardshof to head the other direction as a U11. Conductor told us to just sit tight for a few minutes.... Fortunately it's an above-ground stop!
I'm off work for the next few weeks (between semesters) if anyone wants to go wandering around the city.