One of Sweden’s first real towns. During Viking times, Birka on the island of Björkö in Lake Mälaren was the central hub and the most important marketplace in the entire Mälar Valley. It was established in the mid-eighth century, attracting travelers from near and afar. Birka of today has a wealth of ancient remains that have been excavated and studied since the 19th century. It was designated a world heritage site by UNESCO in 1993. Birka is only open during the summer season, May-September, but can be easily reached by taking a tour with Strömma's Birka-boat from central Stockholm. The trip takes roughly 2 hours.