The grand historic Oscarsborg Fortress stands on Kaholmene in the Drøbak Strait, the Region of Follo. The fortress has been there for more than 350 years, build as a Coastal fortress year 1643-1644, and its name was given by royal resolution on August 23, 1855 after a visit by the Swedish/Norwegian King Oscar 1.
Oscarsborg is best known for the sinking of the German battleship "Blücher" on the 9th of April 1940, ww2, and one can still get a whiff of the creosote (lignite tar) from the battleship.
Oscarsborg Fortress was military territory until 2003, but then made a publicly available resort island.
Today there is an hotel with Spa at the island, Oscarsborg Hotell & Spa, restaurants, Oscarsborg Museum and an event management company, Naturlig Lederskap AS.
You can visit this grand attraction from Oslo båtOpplevelse AS - Sightseeing boats (with daily departure from the Oslo City all year round) or you can take the small ferry from Drøbak.
A preview of Oscarsborg ("Lysbildevisning" means "View slideshow"):