In the 9th Century, Birka was a busy trading metropolis where the Benedictine monk Ansgar was sent by Emperor Frank to convert the Nordic heathens. A visit to this island will reveal the ongoing excavations, and you'll be able to explore the recently inaugurated museum. Guided tours are arranged, which gives you a detailed information on the excavations. You may also get a glimpse of one of the Viking ships, a reconstruction of the ancient seafarers' vessels.