Viljandi castle was one of the strongest castles in Livonia. The construction was started 1224 under Teutonic Order in place of a former hillfort. The crusaders of Sword Brethren conquered the hill fort at the place of later main castle in 1223. A year later, construction of stone fortifications started. Viljandi was chosen as the high seat of the order.
The convent house, a typical form of castle of Teutonic Knights, was erected late 13th – early 14th century. In the following centuries the castle was extended and fortified further. It was badly damaged in the Polish-Swedish wars in early 17th century and not repaired any more. In 18th century, the ruins were used for quarrying stones for construction work in Viljandi.
The first excavations in the castle were performed in 1878–1879. In recent decades, these have turned to almost yearly events. Currently the ruins form a popular resort area just outside of central Viljandi. An open-air stage is located in the former central courtyard.
Reference: Wikipedia
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.