Stieg Larsson's phenomenally-successful Millennium series has already boosted interest in Swedish capital Stockholm, and now even cruise lines are getting in on the act.

Crystal Cruises announced January 31 that it will begin offering shore excursions on some of its European cruises this summer, in an attempt to capitalize on the interest generated from the Millennium trilogy.

The excursion takes guests to Sodermalm, for a walking tour to see many of the places frequented by Larsson's heroes Mikhail Blomkvist and Lisbeth Salander, with Crystal promising that it will be "spiced with factual information and intriguing stories that tie the real Stockholm to Larsson's works of fiction."

Passengers on board three summer Baltic voyages from Crystal Serenity will be offered the tour excursion when the ship stops for its overnights in Stockholm.

Crystal will charge $118 (€85) per person for its excursion and it's not the only one trying to cash in on the appeal of the Millennium trilogy, although there are plenty of ways to see Larsson's dark, mysterious Stockholm for less.

Stockholm City Museum runs its own two hour walking tour for fans of the book, which takes in the Millennium editorial office, Lisbeth Salander's luxury apartment and plenty of other locations, for 120 SEK (roughly €13).

Travelers feeling more adventurous could even create their own, using free online maps such as that on the Stieg Larsson fan site - perhaps with the aid of one of the many Millennium-themed maps available in the city for around €5.