The Viking settlements Birka on the island of BjÃ rkÃ and HovgÃ rden on the neighbouring island AdelsÃ have been a UNESCO World Heritage Site since 1993 , as has Drottningholm Palace on the island of LovÃ n. The Viking age settlements Birka on the island of BjÃ rkÃ and HovgÃ rden on the neighbouring island AdelsÃ have been a UNESCO World Heritage Site since 1993 , as has Drottningholm Palace on the island of LovÃ n.