Dominating a forested hill, this crowning citadel of Halden was built in 1661 by King Frederick III to protect the Danish-Norwegian kingdom against sieges from Sweden, which had already unsuccessfully attacked Oslo and Copenhagen. The king called in engineers from the Netherlands to build what he hoped -- successfully so -- would become an impregnable fortress. It took 10 years for the Dutchmen to create this network of labyrinthine passages and perimeter walls so thick they could withstand cannonballs. The gates were also heavily fortified, as were the bastions. They designed the complex of buildings in the shape of a star at the highest point in the sprawling town along two ridges.

In a former prison in the eastern curtain wall, you'll find the War History Museum. Exhibits depict the history of battle in Halden from the 1600s through the Nazi takeover in 1940. Another museum, Byen Brenner ("the town is on fire"), explores the history behind the town's unfortunate nickname.

An apothecary has been installed in the former Commandant's Residence, which dates from 1754. Modern exhibits trace the history of pharmacology from early folk remedies that relied on bird claws to 20th-century advances in medicine. Bakery and brewery exhibits are also housed within the complex. The bakery could turn out bread for some 5,000 men, and the brewery could produce 3,000 liters of beer a day.

There is no more idyllic place for lunch in Halden than at the fort's own Fredriksten Kro, a mellow old pub with outdoor seating in fair weather.

To reach the fortress, take the steep footpath beginning at Peder Colbjørnsens Gate going up to the principal gatehouse. The stronghold is still in use by the Norwegian army, so not all of the complex can be visited. You can easily spend 2 hours here, although most visitors absorb it in less than an hour.

The Mysterious Death of King Karl XII -- You can see a monument within Fredriksten Fortress marking the spot where Swedish King Karl XII was shot during a 1718 siege. Many Norwegian guides tell you that it wasn't their countrymen who killed the king, but one of his own men. A warmongering monarch, Karl had exhausted his troops and tested their loyalty on the battlefield. Many soldiers were tired of him and his endless battles. It has never been proven where the fatal bullet was fired. Swedes maintain that a soldier within the fortress killed Karl. There is strong speculation, however, that he was assassinated by a Swedish soldier eager to return to home and hearth.

Keep Your Eye on Your Kid -- One thing prevents the Fredriksten Fortress from being truly kid-friendly: The towering bastions are not fenced in and can be dangerous. If you visit with your children, make sure to watch over them carefully.