During the first world war the secret Boden Fortress was completed with its five very huge forts blasted into mountains surrounding Boden city in northern Sweden. They all were abunded as late as in 1998. The Rödberget fort is now a major tourist attraction in Boden. Björn, SM0YUZ knows a lot of these places and he took me on a guided tour to some of them. Many photos can be seen here (sorry text in Swedish) and here you can read the fascinating story of Boden Fortress.
Björn, SM0YUZ standing in front of the huge Stora Åberget fort.
The ugly Radiobunkern in Boden Fortress is a historical site as it was from here in 1921 the first public broadcast programmes in Sweden were transmitted. Link to an article in a Swedish newspaper.