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 Goseck circle is a Neolithic circle structure. It may be the oldest and best known of the Circular Enclosures associated with the Central European Neolithic. It also may be one of the oldest Solar observatories in the world. It consists of a set of concentric ditches 75 metres across and two palisade rings containing gates in places aligned with sunrise and sunset on the solstice days.
Its construction is dated to c. 4900 BC, and it seems to have remained in use until 4600 BC. This corresponds to the transitional phase between the Neolithic Linear Pottery and Stroke-ornamented ware cultures. It is one of a larger group of so-called Circular Enclosures in the Elbe and Danube region, most of which show similar alignments.
Excavators also found the remains of what may have been ritual fires, animal and human bones, and a headless skeleton near the southeastern gate, that could be interpreted as traces of human sacrifice or specific burial ritual. There is no sign of fire or of other destruction, so why the site was abandoned is unknown. Later villagers built a defensive moat following the ditches of the old enclosure.
The Goseck ring is one of the best preserved and extensively investigated of the many similar structures built at around the same time. Traces of the original configuration reveal that the Goseck ring consisted of four concentric circles, a mound, a ditch, and two wooden palisades. The palisades had three sets of gates facing southeast, southwest, and north. At the winter solstice, observers at the center would have seen the sun rise and set through the southeast and southwest gates.
Archaeologists generally agree that Goseck circle was used for observation of the course of the Sun in the course of the solar year. Together with calendar calculations, it allowed coordinating an easily judged lunar calendar with the more demanding measurements of a solar calendar.