Drottningskär Citadel stands as a testament to Sweden's historical might, with construction predominantly occurring in the late 17th century. Revered as one of the nation's premier defence structures, this fortress remains remarkably preserved, offering a glimpse into Sweden's past as a formidable power. Crafted from enduring granite, the large castle encompasses a gun deck, powder magazine, and living quarters, all organised around four bastions named after queens Maria, Christina, Hedvig, and Ulrica. Although it hasn't played an active role in Swedish defence since 1895, Drottningskär Citadel remains a compelling destination. Accessible year-round via the car ferry to Aspö, visitors can explore this historical gem and immerse themselves in Sweden's military legacy.

This fort has defended the entrance to Karlskrona for more than 300 years. Kungsholms Fort is still operational within the Swedish defences. The remarkable round harbour has become somewhat of a symbol for Karlskrona’s status as a World Heritage site. Exotic plants from all corners of the globe flourish under the protection of the fort’s walls. They have been brought here over many years on vessels returning from distant voyages. A museum on the island depicts the fort’s history. There are regular guided tours to Kungsholms Fort during the summer, visits can also be arranged for groups and individuals at other times.