Fjallgatan is the natural extension to the Katarinavagen walk, continuing your way east on the ridge that dominates the coast of Södermalm Island in Stockholm.
The walk will give you on the best views of downtown Stockholm, so make sure your camera's ready. You'll also be able to see Djurgården across the water and get a good look at Gröna Lund's rides!
You can always make your way back to Katarinavägen and then follow Renstiernas gata into the heart of Södermalm, grab a meal at one of the many restaurants along Folkungagatan and make your way back into the city through Götgatan.
APPROX 20 MIN WALK FROM T-CENTRALEN