If you're looking for something to do in Stockholm during the cold season, definitely do a tour of…read moretheir underground subway system! You can book guided tours, but you can also do a self-guided tour for free!
I suggest googling self-guided tours on Google and finding a tour that sounds most interesting to you. You normally start at T-Central and work your way up and down the green, blue, and red lines. There is so much to see, I definitely recommend!!
New York city subways could NEVER. These subways are unmatched, fun, and gorgeous! If you are exploring the subways yourself, I would give yourself 2 hours and buy the 75 minute ticket :)