I suppose it all boils down to your interests. Bars and pubs are not difficult to find anywhere but Swedish ballet or opera, that's a different story. In the Royal Opera house you can see opera, classical ballet, modern ballet, as well as listen to concerts in some of the side halls.
The interior of the opera is beautiful, with marble staircases leading to each level. Prices of tickets vary greatly, and the tourist center on Sergels Torg Square can be very helpful if looking to get tickets or information.
You can also check the website www.operan.se
I am putting this under nightlife since most people go to the theatre at night, I think....This is theKing's Dramatic Theatre in Stockholm. I managed to get this pic while on a bus that was stopped at a bus stop. This is definitely someplace I would like to see the inside of, as long as there's not a dress code! (I've found packing a ball gown for international travel is not a very practical idea!)