If you want to do more than just going out for an easy run there are some good options available.
If you want to test your fitness against local runners; the free group run Haga parkrun is available.
Running in a new city in the winter time can be tricky. Bad weather and darkness makes it hard to find good places to run.
Hagaparken is suitable for running year round and has electic lighting.
If you prefer trails you can check out Ursvik Xtreme.