Balmburg

The ruins occupy a shallow cave cut into an overhanging conglomerate rock face on the western slope of the Sanzenberg, at about 514 metres above sea level. The cave recess extends roughly twelve metres into the rock and its mouth once was closed by a substantial masonry barrier. That closure wall was built of rounded fieldstones and measured about 1.8 metres in thickness, following the line where water drips from the overhang. Only fragments of this wall survive at the sides, and across the front only the foundation course remains visible.

Directly above the cave mouth, the rock shows a soot-darkened band in which squared tuff blocks are set, providing evidence that the upper portion of the cave was formerly sealed by a masonry vault. On the rock face there are clear marks where beams were supported, indicating timber elements once tied into the masonry above the entrance. These ashlar blocks and beam sockets are visible in situ today.

Excavations uncovered a compact deposit of charcoal roughly twenty-five centimetres deep within the interior deposits, and the upper edge of the cave shows soot-blackened tuffstone, both consistent with destruction by fire. The small artefacts recovered during the mid-19th century investigations demonstrate continued use of the site into the later medieval period.

A distinct rock outcrop just to the south of the cave has been interpreted as a likely lookout position, providing a vantage over the Bachsertal. The overall arrangement of cave, entrance masonry and adjacent rock features resembles the layout seen at the Grottenburg Riedfluh near Eptingen, a cave castle rediscovered in 1968 and later excavated and restored.