He was steering without any plan or time pressure, the way he preferred it, just leaning into the boat’s movements and letting the wind squeeze morning tears from his eyes. Trekroner Sea Fortress came into view ahead of him, the small island smiling red and green and invitingly in the sunlight. Mads Teigen steered the fort’s tug familiarly into the little harbor. One lone wooden yawl was moored by the dock, otherwise the harbor was empty. He tied the boat securely, turned off the motor, and jumped ashore. The steep embankments were covered with spring grasses that looked like soft wings of wild-growing green and yellow protecting the old fort.

Trekroner was originally built in 1713 as part of Copenhagen’s fortifications, a system of defense structures that included several other forts and which played a key role in legendary attacks like the 1801 Battle of Copenhagen and the 1807 British bombardment of Copenhagen, when the city lost its fleet. The original fort of Trekroner was established with three old ships that were sunk and filled with rocks. One of them was named the Tre Kronor, and she gave her name to the fort even though most people think it originates from the time, over 250 years later, when the island was sold to the government for three Danish kroner.

Mads picked up a stray plastic bag and scanned the horseshoe-shaped promenade for signs of life but didn’t see any. As always his eye lingered on the white lighthouse, which towered over the main entrance to the fort itself. From there the structure extended down two stories belowground. The casemates had served as a base for 750 soldiers during the First World War, and the Germans later used them during the occupation. When standing within those peeling walls in the corridors below sea level, you could still sense the smell of gunpowder and anxious sweat in the air. Panic and boredom had seeped into the masonry and now whispered the tales of hundreds of dead men.

Nowadays the fort was home to only birds, mink, and one solitary fortress caretaker living in the red-painted old commandant’s quarters. A hermit on his island—that had become his fate.

Mads walked across the platform, where he was amassing wood for the midsummer bonfire, and up over the ridge to the outside of the embankment. He wanted to check on the pair of swans that was nesting down by the breakwater. From the top of the embankment the view of Copenhagen’s towers and spires on the one side and Malmö’s Turning Torso on the other was unimpeded. Standing there, he might as well be on his own planet, it was that deserted. An enclave of wilderness in the middle of the capital, separated from the hectic city life by only a narrow band of water.