Alter Bau, Historical building in Geislingen an der Steige, Germany.

Alter Bau is a 21-metre, eight-storey half-timbered house built around 1445 in the old town of Geislingen an der Steige. Its Alemannic timber frame shows widely spaced posts, continuous lintel and breast rails, and swallowtail-jointed diagonal braces. The ground floor was later rebuilt in tuff stone. Today it holds the Museum im Alten Bau, a gallery, and the Southwest German Treasure Chest Museum.

This building was constructed around 1445 by the Imperial City of Ulm as a granary after acquiring the area from the Counts of Helfenstein in 1395. Its construction marks when Ulm expanded influence over the region and created local structures to support trade and administration.

The building's name, Alter Bau ("old building"), comes from its long service as a granary; grain was stored on its six lofts until 1860. The museum's collection highlights the Geislingen bone-turners and ivory carvers, a craft that shaped the town's trade for centuries. The gallery on the ground floor has shown art exhibitions since 1985.

The museum is easily accessible by foot through the old town and offers both permanent exhibitions and rotating art displays that change seasonally. Special decorations and displays appear during the Christmas season, giving visitors an additional reason to visit during the holiday period.

The bird display "Unsere Vogelwelt" opened in 2017 and draws on more than 250 specimens collected by Dieter Rockenbauch, used to explain local habitats, species diversity and nature conservation. It is the newest department of the museum, added after the city-history and treasure-chest sections.