Oscarsborg Fortress

Oscarsborg is a coastal fortress spread across two small islets, Nordre Kaholmen and Søndre Kaholmen, with additional artillery batteries on Håøya island and the mainland. The site features underground tunnel networks, gun emplacements, and various structures that demonstrate its defensive capabilities.

The fortress was built in the 19th century as a defense against seaborne attacks and played a crucial role in 1940 when attempting to slow the German invasion. The attack on the German warship Blücher marked a turning point in the first hours of Norwegian resistance.

The museum displays military exhibitions, while the grounds host theater performances, opera shows, and concerts during summer months. Visitors experience a blend of history and contemporary culture at this historic location.

The site is accessible by ferry from Drøbak or Oslo, with guided tours available through the tunnel system. Visitors should prepare for uneven ground and tight passages, especially when exploring underground areas.

A secret torpedo system with an underwater launch mechanism remained hidden from German intelligence during World War II. This technology allowed the fortress to engage ships without revealing its positions.