The fortress of Kristiansten is not very attractive in appearance since it has a simple architecture. However, it is one of the most important attractions in Trondheim because it has a rich and important history.

Construction of the fortress began in 1682 by order of King Christian the Fifth. It was immediately clear that this would not just be a defensive structure but a stronghold of the city, its «fighting heart» which would show the power and significance of Trondheim.

The fortress consists of three high floors and a specially fortified powder crawl space. The first floor contained the commander's rooms, a living room, a kitchen, and two cells for prisoners. The second and third floors were defensive. There were guns placed in a special order. At the very top on the roof of the tower, there was an observation post.

The fortress of Kristiansten experienced a lot. It withstood a huge number of sieges and did not fall. The most famous blockade was in 1718 during the Northern War. The defenders held the fortress for more than six months. They did not allow the Swedes to break into the city, even though the Swedish army had more than 10,000 men. Only after a long standoff, the Swedish army realized that Trondheim would not give up. So it was forced to retreat without reaching the city.

The 19th century was no less difficult for the fortress. In 1816, the king decided that there was no need for a fortress because it was old and no longer performed its functions. He even ordered to dismantle it completely. The only thing that saved the fortress was that it housed cannons that had the function of notifying the city of natural disasters, fires, attacks. There was no other warning system. Therefore, the fortress was left as it was.

Other black days in history were the days of the German occupation. The Nazis shot members of the Norwegian resistance movement at the walls of the fortress. Many brave and talented people ended their lives at the fortress which was the defender of the city. Among them was the famous composer Oskar Hoddø.