Köngen is in the area of the Roman settlement Grinario that was built around 100 AD around a Roman castra. Grinario was the endpoint of the Roman road 'Neckar-Alb-Aare' which originated in Windisch (Switzerland). In 260 the place was destroyed by the Alemanni and the Romans were expelled.
Johann Eberhard Roser discovered some traces in 1782 and started excavations here one year later. At present it is the site of an archaeological park and museum. The earliest reconstructions were those of a Roman corner tower, the originals of which were discovered in 1855. The tower was ready in 1911 and the 'Köngener Römerkastell' with its great viewpoint and small indoor museum soon became a popular excursion.
In World War II and the period short after, the tower was damaged and it was not open to public until 1949. In the 1970s, the tower was fully renovated and a small museum was built next to it.
Visby Cathedral (also known as St. Mary’s Church) is the only survived medieval church in Visby. It was originally built for German merchants and inaugurated in 1225. Around the year 1350 the church was enlarged and converted into a basilica. The two-storey magazine was also added then above the nave as a warehouse for merchants.
Following the Reformation, the church was transformed into a parish church for the town of Visby. All other churches were abandoned. Shortly after the Reformation, in 1572, Gotland was made into its own Diocese, and the church designated its cathedral.
There is not much left of the original interior. The font is made of local red marble in the 13th century. The pulpit was made in Lübeck in 1684. There are 400 graves under the church floor.