The pubs and bars in Södermalm range from extremely shady to outrageously chic. Point is, there are loads of them. There’s no island in Stockholm with as many bars and pubs.
The area around the square Mariatorget is one of the nicest neighborhoods in Stockholm, with trendy cafes and hipsters everywhere you turn. On the opposite side of Södermalm is Nytorget. This neighborhood is also, quite ridiculously, called Sofo (South of Folkungagatan). If you actually call this area Sofo in a conversation with someone who is trendy (or think they are trendy) they will probably perceive you as extremely untrendy.
There’s a large cluster of nightclubs around the square Stureplan. Everyone who’s drunk in Stockholm ends up here sooner or later, because it’s one of the only few areas where the clubs are allowed to be open past three A.M (03.00). Östermalmstorg is a nice square with lots of posh cafes and restaurants. Here you will also find the posh and upclass market Östermalmshallen, where all the rich old ladies buys their foie gras.
Strandvägen is one of the most popular and beautiful promenades in Stockholm. It runs from the Royal Theater to Djurgården (large park). If you have a few hours to kill before dinner, this is a really nice walk.
Needless to say, people from Södermalm and Östermalm usually chose not to mix. Old Town is like a buffer zone between these two neighborhoods as they glare at each other across the water. Japes aside, the two isles represent two very different sides to Stockholm and they are both worth a visit.
Major tube-stations: Östermalmstorg (red line), Karlaplan (red line)
Major tube-stations: Odenplan (green line), Rådmansgatan (green line)
Riddarholmen is a tiny island just off Old Town and it is home to several of the oldest buildings in Stockholm, most notably Riddarkyrkan, where many of Sweden's old monarchs lay buried. Other than that it's pretty barren from points of interest.
I have to be honest with you, Kungsholmen is not a part of town I frequent a lot. It used to be known under the not so flattering name “Retirement Isle” a couple of decades back due to the many senior citizens living here. The Florida of Stockholm if you like. Now-a-days much has changed (old people does not stay old forever you know) and Kungsholmen is much more trendy and youthful. The park Rålambshovsparken is probably the largest outdoor drinking hangout for youths. Bring a six pack and feel right at home.
The majestic Norr Mälarstrand is a long boulevard that runs along the southern shore of Kungsholmen and there are a lot of nice outdoor restaurant and bars along this shoreline, most notably Mälarpaviljongen (gay friendly) and Restaurang Kungsholmen (up class). City Hall is situated at the beginning of Norr Mälarstrand, and it’s worth a visit (this is where they hold the Nobel Prize dinner).
This is actually part of Vasastan, but for some reason it is considered to be an independent enclave. Birkastan is an old working class area with loads of cafes and restaurant. Sometimes it’s called “Little Paris” because of all the cafes, but that’s just something I reckon some realtor made up to increase market values. It's small, it's cosy, you'll love it.
Major tube-station: St. Eriksplan (green line)
Other isles, big and small
Djurgården is a large island close to Östermalm. It’s like a huge park, but there are also a few residential areas and some extremely exclusive villas out here. It’s also where you will find the Gröna Lund amusement park and the zoo Skansen. There's a huge outdoor bar/night club in Djurgården called Josefinas. It is not super trendy, but it's a nice place to go for a few drinks because of the view. There are also loads of museums out here, most notably the Vasa Museum. You get to Djurgården by tram from Sergelstorg or Norrmalmstorg.
Blasieholmen, Skeppsholmen and Kastellholmen is a series of small isles. Blasieholmen is where Grand Hotel is situated so it’s pretty easy to find and very central. Most boats to the archipelago leaves from here. Blasieholmen and Kastellholmen are both very pretty with lots of museums, nice restaurants and walks along the waterfront that promises good photo ops.