Oscarsborg Fortress

Oscarsborg Fortress sits on the islands of Kaholmen in the narrow Drøbak Sound, guarding the maritime approach to Oslo. Although its origins reach back to the mid-19th century, the fortress entered history on the night of 9 April 1940, when it opened fire on the German heavy cruiser Blücher during the opening hours of the invasion of Norway.

The fortress’ aging artillery — notably the 28 cm guns nicknamed Moses and Aaron — combined with torpedoes launched from an underground battery, fatally damaged the cruiser. Blücher sank with heavy loss of life, delaying the German advance and giving the Norwegian government and royal family crucial time to escape Oslo. The event transformed Oscarsborg from an obsolete fort into a symbol of resistance.

Today, Oscarsborg is both a military monument and a memorial landscape. Visitors can explore gun batteries, underground tunnels, and prison areas, while the calm waters of the fjord contrast sharply with the violence of 1940. The site’s power lies in this tension: a peaceful setting that once decided the fate of a nation in a single night.