The floor is trembling, the prisoners are crying, and the evil Sargent Stålhammar is not far away. Karlsborg Fortress has its very own 3D treasure hunt for children during the summer months.

The children are lead on an adventure through the dark dungeons of the fortress in search of a hidden gold treasure. The tour has been planned for two years and includes a 3D film that introduces the adventure.

- That's what makes it so unique. We mix the latest technology, 3D film and motion controlled computer games, with this old environment. Together they really create a feeling of being in the midst of an exciting adventure, says Jan Dahlqvist, project manager for Karlsborg Fortress, to GP.

- It was great fun, especially to run around in the fortress when you could hardly see anything, says one of the adventurers, Albin to GP.

But for some the adventure almost gets too realistic.

- It is a balance act; we want to create a sense of that this is for real. And it should be exciting. But some children may think that it is a little bit too scary, says the guide Miranda Jonsson to GP.

The construction of the Karlsborg Fortress started in 1819 and it took 90 years to finish. When Sweden lost Finland to Russia in the war 1808-1809, Stockholm became a frontier town and more vulnerable than before. Therefore it was decided that Sweden needed a fortress next to the lake Vättern and close to the Göta River. The idea was that the government, the Royal family and the gold reserves would be moved there in the event of a new war.

The interactive 3D tour runs several times a day all summer.

You can also travel back in time at for example:

The Hova Medieval week, from July 9-17. The whole village turns medieval for one week - the park is crowded with market stalls, knights in shining armour, witty jesters and musicians. Both locals and visitors dress up in medieval clothing to fit into the atmosphere.

The Stone Age week at the Ekehagen prehistoric village (located south of Falköping), from July 13-20.

Kungahälla Medieval Days at Bohus Fortress in Kungälv from July 22-24. The festival is held for the ninth time in a row and has grown to become one of the largest medieval festivals in Sweden.

Medieval Days at Torpa Stenhus in Länghem (east of Borås), from July 23-24.

Sweden's oldest Viking Market Hornbore ting, at Hornborgs slott in Hamburgsund, from August 5-7.