The remains of the fortress can be visited
Poel Fortress

Poel Fortress is located on the island of Poel in the municipality of Kirchdorf. Originally designed as a castle complex, it had star-shaped architecture and a system of moats and earth ramparts.
History+
Construction of Poel Fortress, including a castle, began in 1614. Duke Johann Albrecht II of Mecklenburg commissioned the construction after securing lands on Poel Island and other estates. Under the direction of master builder Gerhart Evert Pilooth, a two-part structure emerged: a star-shaped castle and a so-called “Hornewerck” in the form of a star tail. The latter housed the church, soldiers' quarters, the captain's residence, and stables, all surrounded by a system of moats and eleven-meter-high earth ramparts.
Source: Wikipedia · Licence: CC BY-SA 4.0 · Image: Roland Neubert, Halle (Saale)
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: 53.9931, 11.4374