The Altenburg is a castle that sits on the tallest of the seven hills of Bamberg, southern Germany, overlooking the town.

This is a castle that was not regularly inhabited, but served mainly for city defense as a place where local residents could flee to in times of danger.

In 1801, the Bamberg physician Adalbert Friedrich Marcus acquired the decaying castle and restored it from the ground up.

The author E. T. A. Hoffmann, who was friends with Marcus, felt so drawn to the castle that he frequently stayed for a long time in one of the wall towers during the years 1808 to 1813.

From 1952 to 1982, a brown bear named Poldi lived in a Zwinger (a defensive enclosure) in the castle.