A friend is visiting Stockholm for a weekend, also called for it beauty the "Venice of the North". The tour usually starts in "Gambla Stan", the old town that keeps buildings and streets from the fifteenth century with a clear Scandinavian spirit. The Royal Palace is awesome, and the morning guard shift is one of the most traditional events in the city. It is worth having a walk around its well-preserved medieval streets and visit the Cathedral, the Stock Market and the typical shops and restaurants.
From Gambla Stan, there is a magnificent walk through the canal to the north into Norrmalm: the Royal Opera, the Grand Hotel (where the Nobel Prize winners are hosted), Operakällaren (exceptional traditional restaurant), and other beautiful buildings, Gustav Adolfs Torg and Kungsträgården, a beautiful garden, the most lively green space in the city.
A longer walk to the east leads to Djurgården, where we find the Vasa Museum, the most visited museum in Sweden, dedicated to a wreck that occurred just outside the harbor on the maiden voyage in 1628. Also here is Skansen, the world's oldest outdoor museum including a zoo, traditional Swedish craft exhibitions, restaurants, etc.
Heading west from Gambla Stan, you find the City Town Hall where the Nobel Prize Annual ceremony takes place. Further away you can go for a walk in Norr Mälarstrand, where you can have a coffee in a nice café and sunbathe in the hot summer days.
Southern Stockholm has become trendy in recent years, representing the bohemian area, and of course, where you find the "house of Mikael, Lisbeth´s favorite bar ..." so, the neighborhood where the famous trilogy by Stieg Larsson Millennium develops.
If your stay is extended beyond a weekend, it is worth visiting the university town of Uppsala, the Drottningholm Palace (in the style of Versailles) and Mariefred and the Gripsholm Castle. There are tourist boats that reach Mariefred, and you get the chance to enjoy magnificent sights from the archipelago.
The best time to visit Stockholm with good weather is from May to September, although I would recommend to always have a raincoat handy. The end of June, around midsommar, offers the most festive face of the city. Also, during the month of December, you find the traditional Christmas market in Gambla Stan where you can buy the typical Nordic Christmas decorations. There are a wide range of restaurants where you can try Swedish food and the famous Smörgåsbord. If you have the chance, Stockholm will not disappoint you. Bon voyage, my friend!