The Swedish destroyer HSwMS Uppland inside one of the tunnels of the underground Muskö Naval Base. Muskö Naval Base was an extensive underground Naval facility, equipped with a number of facilities. It had three docks, designed primarily for submarines and other smaller warships. Sweden had begun deactivating parts of the base during a redistribution of its naval forces In the mid 2000s. However, in 2020 it was decided that the base would be fully reactivated. Photo from the Swedish Naval Museum.