Hammersta castle was a 13x18m wide two-storey stone building built around the year 1300 by Eringilse Nilsson, who's father was married to a sister of Bridget of Sweden. Eringilse's son (with the same name), was married to a Danish woman, Brita Olofsdotter Tott, and when the situation between Sweden and Denmark became tense around 1450, Tott was sentenced to death for spying for the Danes. Luckily for Brita she was pardoned and later paid for the famous fresco paintings that you can now see at the Ösmo Church.
The castle was abandoned in the 15th century. Between 1628 and 1767 the estate was owned by Horn, Kruus and Wrede families. The new manor house building was started in 1685 and completed in 1723.References:
The Externsteine (Extern stones) is a distinctive sandstone rock formation located in the Teutoburg Forest, near the town of Horn-Bad Meinberg. The formation is a tor consisting of several tall, narrow columns of rock which rise abruptly from the surrounding wooded hills. Archaeological excavations have yielded some Upper Paleolithic stone tools dating to about 10,700 BC from 9,600 BC.
In a popular tradition going back to an idea proposed to Hermann Hamelmann in 1564, the Externsteine are identified as a sacred site of the pagan Saxons, and the location of the Irminsul (sacral pillar-like object in German paganism) idol reportedly destroyed by Charlemagne; there is however no archaeological evidence that would confirm the site's use during the relevant period.
The stones were used as the site of a hermitage in the Middle Ages, and by at least the high medieval period were the site of a Christian chapel. The Externsteine relief is a medieval depiction of the Descent from the Cross. It remains controversial whether the site was already used for Christian worship in the 8th to early 10th centuries.
The Externsteine gained prominence when Völkisch and nationalistic scholars took an interest in the late 19th and early 20th centuries. This interest peaked under the Nazi regime, when the Externsteine became a focus of nazi propaganda. Today, they remain a popular tourist destination and also continue to attract Neo-Pagans and Neo-Nazis.