Stockholm is a maritime city, so we found ourselves on ferries on several occasions. Especially during the summer season, ferries offer convenient shortcuts between the major islands. In the city centre, you'll see antique Djurgården pedestrian ferries zigging and zagging through the harbour almost constantly. These antique ferries carry some 2.4 million passengers a year, primarily in summer.
The Djurgården-Skeppsholmen-Slussen line is open year-round. From mid-May through mid-August, ferries also run at 20-minute intervals between the main Djurgården pier, the Vasa Museum, and Nybroplan near downtown Stockholm. This route operates on weekends only during early May, late August, and September. Fares are rather steep, but you can ride free with a Stockholm Card. Stockholm Card buyers also get a discount on Stromma Kanalbolaget sailings to Drottningham Palace. Strömma Kanalbolaget also has archipelago tours aboard the 1912-vintage Gustafsberg VII.
Stockholm Sightseeing is a company that offers a good selection of boat tours, including a "hop-on hop-off boatseeing" service. Some tours are available free or at a discount with the Stockholm Card. Hop-on and hop-off at the various bridges as often as you like, or stay onboard and enjoy the ride. The ticket is valid for 24 hours and it can be combined with the open top bus tour. Guided onboard narration is included.
Your boat takes you to the Royal Palace where you can watch the changing of the guard. At the Nybroviken terminal, which is a short walk from the shopping district, you can take another boat to Fjaderholmarna and Djurgarden. If you have your mind set on history, you don't want to miss the Vasa museum and Nordiska Museum. Then there is the classic amusement park Grona Lund or visit Skansen with its variety of traditional buildings and wild animals. Historic buildings are also to be found in Gamla Stan. Even though they were built during the 17th and 18th century they are very well preserved.
There are many other tours to choose from depending on your interests. Under the Bridges of Stockholm, Royal Canal Tour, Historical Canal Tour, and the early Good Morning Stockholm Tour concentrate on central Stockholm and take from 50 minutes to 2½ hours. The Good Morning tour is given in Swedish and English only. Other tours are given in more languages. The number of tours is limited during the winter, however.
Archipelago Race is for those who want to see the archipelago but do not have much time. In a fast Speedo boat, you get a feel for the archipelago and its 28,000 islands in less than 2 hours. The tour is given in Swedish and English. Tickets can be purchased online.