Sigtuna is on the distance of 40 kilometers from Stockholm. It is possible to pass there by car on motorway Å4 in a direction of airport Arlanda. The airport will appear at the right, and a turn to Sigtuna - to the left. Then it is necessary to pass 8 kilometers to the place. A free-of-charge (!) parking is available in the city centre.
Public transport - travel from Stockholm up to the station of underground "Marsta", further by buses 770, 575.
I heard, that it is possible to reach Sigtuna by ship through the Melaren lake.
If you don't have a car, the bus is the quickest way to get you to and around Sigtuna. From Märsta station there are 2 bus lines going there: 570 and 575 and the trip takes about 30 minutes. Check their timetables and stops at the link below.
If the weather is nice and you have a bike, this might be a good way to get around (or to) Sigtuna. A map of Sigtuna's bike network is available at the link below. When the page has finished loading, click on "Cykelkarta.pdf (obs stor fil)" on the right (the address wouldn't load correctly).
If you buy the Stockholm Card in Stockholm you'll have access to all the buses, subways and commuter trains in Stockholm.
With this card you can easily go to Sigtuna. Take the commuter train from Stockholm central towards Märsta, it takes 37 minutes.
From there you take the connecting bus 570 or 575, it takes 20 minutes.
In the summer time you can go by boat from Stockholm on the cruise "Kungsleden" that makes stops in Sigtuna, Skokloster and Uppsala.
Many of you might already have been to Sigtuna without knowing it as this is where Stockholm Arlanda airport is. However, the airport is in the eastern parts of the district whilst Sigtuna town itself is down by Lake Mälaren. Because of Arlanda, flying is an easy option and most western airlines fly to Stockholm as do several others.
If you find yourself in Stockholm, there are two ways of getting to Sigtuna. In summer, you can catch a boat from the City Hall but then you are sometimes limited to a daytrip. If you want to explore the town on your own, go by commuter train from the Central Station to Märsta and then catch a bus. A bit of a trek but certainly worth it!
The commuter train from Stockholm to Marsta takes 35 minutes. It runs twice an hour. From Marsta, take a bus no. 570 or 575.
You can get on both commuter train and bus with SL card.