The remains of the fortress can be visited
Fortress Magdeburg-Zwischenwerk VIa

Intermediary Work VIa is a preserved element of the Fortress Magdeburg, which from the 18th to the early 20th century was among the most significant Prussian defensive structures. Located in Magdeburg, Saxony-Anhalt.
History+
The origins of Magdeburg's fortifications date back to the 13th century. With the advent of firearms in the 15th and 16th centuries, the installations were modernized and expanded to meet military requirements. This included the construction of a second city wall, the fortification of the Elbe front, and the erection of new city gates with gun towers. The fortress proved effective during sieges, such as those of 1550/51 and 1629. During the Thirty Years' War, it was expanded under Swedish command, but neglect of the southern front led to the city's capture and the dismantling of the installations in 1631. From 1666, Elector Friedrich Wilhelm ordered its reconstruction, which continued under Prince Leopold I of Anhalt-Dessau and later under fortress master builders von Bosse and von Walrave. Around 1740, Magdeburg was considered Prussia's strongest fortress. Nevertheless, in 1806, it fell to Napoleon without a fight.
Source: Wikipedia · Licence: CC BY-SA 4.0 · Image: http://commons.wikimedia.org/wiki/File:Magdeburg_Zwischenwerk_6a.jpg
This description draws on the facts documented in the linked Wikipedia article; Wikipedia content is licensed under CC BY-SA 4.0. Wording and editing: Mobile History.
Location: 52.1609, 11.6242