Are flights the best way to Stockholm? We'd like to do a daytrip or orvernight trip during our vacation to Copenhagen.
This was discussed very recently https://community.ricksteves.com/travel-forum/denmark/should-i-give-up-on-traveling-from-copenhagen-to-stockholm-by-high-speed-train-and-just-fly
The short answer is fly, but since it's a 4 - 4,5 hour trip all included, it's certainly not feasable as a day trip, not even mentioning that Stockholm is a capital city with more than enough to keep you occupied for several days.