Burg Alt-Dernbach, Medieval castle ruins in Seelbach, Germany.

Burg Alt-Dernbach is a medieval castle site in Seelbach consisting of earthen remains and an old fortification mound. The layout stretches approximately 83 meters (272 feet) in length and 60 meters (197 feet) in width, with a moat system that once surrounded the defensive structures.

The lords of Dernbach sold their castle rights to the Counts of Nassau in 1333, ending their rule in this region. This transaction marked a shift in local power and the territory's integration into the Nassau domain.

The name Theyrinbach appears in a 1263 charter of Marienstatt Abbey, in which the knight Bernhard von Dernbach granted the monastery a tithe. Locals later called the mound Butschel, and the site is also recorded as Burg Dernbach or Purzel. A sheep farm now stands on the old castle grounds.

The site is currently fenced off and closed to visitors, as it operates as a grazing area for livestock. Respect the barriers and observe the location from the outside to avoid disrupting the land's current use.

Archaeological excavations during the 1950s uncovered foundation remnants of a defensive tower that once crowned the earthen mound. The tower's base measured only 3 by 3 meters, while the supporting mound beneath it spanned roughly 22 by 16 meters.