Altenburg, Cultural heritage monument in Weimar, Germany.

Altenburg is a three-story building at Jenaer Straße 3 in Weimar, named after the old field name "Die Alte Burg". Built in 1811 for Oberstallmeister Friedrich von Seebach, it now houses the Franz Liszt Centre of the Hochschule für Musik Franz Liszt Weimar, including the Liszt Salon and a documentation on Liszt, the Altenburg and Europe.

Friedrich von Seebach, who had accompanied Duke Karl August and Goethe on the 1792 campaign in France, had the house built in 1811; its name comes from the old field name "Die Alte Burg". From 1848 Franz Liszt lived here for thirteen years with Carolyne zu Sayn-Wittgenstein, and much of his orchestral music and the symphonic poem were developed here. From 1867 the commanders of Infantry Regiment No. 94 resided in the house.

From 1848, Liszt turned this residence into a meeting place where European composers and musicians gathered to share ideas. The house became known as a hub for musical exchange and creative collaboration during that era.

The building is located centrally in Weimar and easily accessible on foot. Visitors should keep in mind that it functions as an active music school, so access may vary depending on events and class schedules.

In the garden stands a sandstone memorial to Belotte, the dog of builder Friedrich von Seebach, erected in summer 1822. Its inscriptions read "Here rests Belotte. She was faithful to her first and last master", "She saved a human life" and "1808–1822"; she had rescued him in fighting between French and Allied troops on 22 October 1813.