Altenbaumburg, Medieval castle ruin in Alsenz Valley, Rhineland-Palatinate, Germany.

Altenbaumburg is a castle ruin perched on a ridge above the village of Altenbamberg in the Alsenz Valley, in Rhineland-Palatinate. Sections of the outer walls, towers, and foundation structures are still standing on the site.

The castle was the ancestral seat of the Raugrafen. A document of 1253 mentions a "New Castle" near the vanished village of Sarlesheim, which refers to the later Neuenbaumburg, not this site. The name Altenbaumburg appears explicitly in charters from 1324. By 1317 several owners are recorded, making it a Ganerbenburg. In 1681 a source already called it a ruin, and French troops devastated it in 1689.

The castle was the ancestral seat of the Raugrafen, a comital family whose line split in 1214. From 1317 several owners are documented, making Altenbaumburg a Ganerbenburg shared among co-heirs. In 1320 King Ludwig the Bavarian granted the valley settlement below Oppenheim town rights and market rights, yet the family's financial troubles continued.

The ruin is reached by hiking trails that run through the Alsenz Valley and the surrounding hills, open throughout the year. The ground is uneven and the slopes can be steep in places, so sturdy footwear makes the walk easier and safer.

The rectangular keep, or Bergfried, once stood about 40 metres high, making it one of the most powerful of its kind, according to a copper engraving from before 1629. Only a four-metre stretch of its northwest side survives, built of bossed ashlar blocks from the early 13th century and now exposed from a rubble mound in the former courtyard.