The Swedish landscape has extremely beautiful lakes, forests and mountains that are used by most Swedes all year round. Even inside Stockholm it is possible to find a green park or a peaceful lake where one can relax in contact with the nature.
Another thing that makes this city special is the archipelago which is just a short boat trip east out of town. Even though it is very popular among locals during summertime, as the temperature of the baltic sea allows summer baths, the archipelago can also be rather spectacular throughout all seasons.
Utö is a traditional destination, which allow for great walks and bathing (the water temperature in the baltic is around 20˚C in the Summer). Another advantage of being in one of the bigger islands (as Utö) is that if you want to socialize during the evening, just head up for the local pub where there will be some partying going on. For a more calm experience just pick any small island next to Utö like Ålö and Rånö.
Most of the boats leave from the centre of town or Nynäshamn and are one hour away from most islands. Take a newspaper, a book and your camera, head out for a day in an island of your choice and enjoy a delicious meal at one of the great archipelago restaurants before coming back. But if you have the time for it, why not staying an extra day at one of the beautiful inns opened all year round?