Kalmar Castle, dating back 800 years. The last king to actually live in the castle and carry out government business from there was Karl XI, from 1673 - 1692. Kalmar Castle played a very important role in Nordic politics as early as 1397. It was the meeting place for the signing of the Kalmar Union on July 20th 1397. Queen Margareta signed this very controversial act. Kalmar celebrated the 600th Anniversary of the Kalmar Union in 1997.