Nyborg Castle was built around 1170 AD. We don't know exactly what the oldest castle looked like, but the core of the existing palace building is from the mid-1200's, and before that, the ring wall around the castle square had been built. This was the meeting place of the Danish parliament for 200 years.
Nyborg was strategically placed, in the middle of the country, on the water, so King Erik Klipping used the castle to hold gatherings of the most powerful men in the country, the so-called Danehof meetings. At Nyborg Castle, in 1282, Erik Klipping signed his coronation charter, the country's first constitution. It was here that Chamberlain Stig Andersen was stripped of all his rights and deemed an outlaw for the murder of Erik Klipping in 1287. It was also at Nyborg Castle that Queen Margrethe I's son, Oluf, signed the agreements that made him king of Norway, paving the way for the Union of Kalmar, in which the three Scandinavian countries were gathered in Margrethe's hand to become Europe's largest kingdom. The last Danehof meeting was held in 1413.
Nyborg Castle's significance in Danish history is unmistakable: you can, today, walk around the same room, the Danehof Hall, the historic room where the king met with his parliament in the Middle Ages and where Denmark's first constitution was signed. This makes Nyborg the cradle of Danish democracy.