Kastellholmen, islet in Stockholm, Sweden

Kastellholmen is a small islet in the harbor of Stockholm, reached by a footbridge from the neighboring Skeppsholmen. It has a tidy layout with old trees, a walking path along the shore, a hilltop viewpoint, a small castle called Kastellet, a lighthouse, and several former navy houses now used as private homes.

In the 1600s a small wooden octagonal structure with a flagpole stood here, used for storing gunpowder and firing salute cannons as ships entered or left the harbor. After the wooden building decayed and a stone replacement was later damaged by an accidental explosion, the current castle was built between 1846 and 1848.

The naval flag has flown here since 1665, signalling that Sweden is at peace and Stockholm is not under foreign rule. When the military decided to stop the daily hoisting in 1990, the commander of the corvette HMS Stockholm raised it again on 2 April 1990 and fired a salute; the decision was reversed and the flag is raised and lowered every day from 6 June 1990. The castle now serves as an officers' club, and the 19th-century ice-skating pavilion is used for parties and events.

You can reach the islet easily on foot by crossing the bridge from Skeppsholmen, and a stroll around the shore path takes only a short while. The ground is uneven in places, especially if you climb the hill, so comfortable shoes are a good idea.

Until the 1800s, the island announced the city's routine with cannon fire: every evening a single shot was heard across the water as a signal that all was well. A later accident came from a navy experiment that authorities first mistook for an attack, and the rebuilding that followed gave the small castle its current look.