Here you are in front of a small citadel that crowns the islet of Kastellholmen like a medieval castle by the water. This red-brick monument hides a turbulent history spanning more than 350 years. The story begins in 1667 with the first fortification built by Erik Dahlbergh to protect Stockholm’s harbor. But in June 1845, the old structure exploded accidentally, forcing a complete reconstruction. From 1846 to 1848, military architect Fredrik Blom—who also designed the Nationalmuseum—created the new Kastellet in a romantic neo-Gothic style, with its round tower and 20-meter stair turret. After the fleet moved to the city of Karlskrona in 1680, the site lost its importance until World War II, when it regained a strategic role as a point of anti-aircraft defense for Stockholm. The Coastal Artillery School used it until 1990, marking the end of three centuries of military service. Today, the Kastellet is famous for a unique tradition: every morning, soldiers raise the Swedish military flag at the top, a symbol that Sweden is at peace. This daily ceremony makes the little fortress a living emblem of Swedish neutrality. A fun anecdote: in 1996, Norwegian expatriates briefly replaced the Swedish flag with their own to celebrate their national day! Although the interior is not open to visitors, the Kastellet offers from the outside one of the most photographed panoramas of Stockholm. This citadel perfectly embodies Sweden’s transformation—from a major military power to a peaceful nation—reminding us every day that peace remains our most precious treasure.