I have visited only Birka as a half day organized boat tour from Stockholm city hall pier. The trip itself was pretty nice but a bit too long – 2 hours one way. As there’s nothing to do on the boat, it is a good time to read or just enjoy the sunny weather – if it’s sunny of course.
Birka is not a very big archaeological site and, as stated in other reviews, not many things to see – just hundreds of burial mounds and some stone walls rising just a metre or less from the ground. The small museum is included in the tour, although most of more interesting artefacts are displayed in the Swedish History Museum in Stockholm.
We had a one hour guided tour around the island, and the guide was really great! We walked through the mounds and heard the story of Vikings, their everyday life and conquests, their rituals and beliefs. He gave us many info about what was excavated and found in the graves, how their defensive system looked like and what their feared. The tour ends at the rock with a cross commemorating German archbishop Ansgar who came here in 9th century to serve German traders living in Birka.
The biggest value of this inscription (together with Hovgården where the so-called king might have been residing, one of the biggest mound was discovered there) is that was probably the first proto-urban Viking settlement. The amount of burial mounds and footings of wooden houses indicates that at its peak the population numbered around 1000 people. But during the second half of the 10th century Birka was abandoned. And nobody knows why…