Only foundations and one gate-tower have survived of the so-called fortified Tafelgut that used to belong to the bishop of Tallinn.
The castle was erected on a hill by the Porkuni lake in 1479 by Simon von der Borch. Cannon towers stood in the corners of the camp castle shaped as an irregular rectangle. The circular wall and the towers did not probably reach their height all at the same time, but in the course of a longer period. This claim is backed up by the gate tower - rectangular at the bottom and octagonal at the top. The machicolation frieze adorning the top of the tower dates back to a much later time, as proved by comparing the engravings of Porkuni produced in the 17th and 19th centuries. The castle was severely damaged during the Livonian War. The castle tower currently houses museums.
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.