Burg Hauenstein

The castle occupies a hard porphyry rock spur and is laid out along a northeast–southwest alignment. The main enclosure is slightly V-shaped and runs for roughly 35 metres from northeast to southwest, narrowing to about 16 metres at the southern end and widening to about 20 metres at the northern end. Stone walls were built directly on the rock and in places follow the ridge closely, producing a compact, elongated complex that adapts to the natural outcrop.

Approach and external defences survive as earthworks and cut ditches. The historic road reached the castle from the southwest, where a deep pointed ditch lies to the left of the path. Two further ditches fronted the castle and were partly backed by an earthen wall; the southwest side was defended by a combination of ditch and rampart, and an additional ditch runs before the northeast face. These cut features were integral to access control and to the later defensive layout.

A man-made pond northwest of the castle formed part of a water system fed by a weir that brought water from Hochsal, located about two kilometres away. Remnants of that weir remain visible, and overflow from the pond was channelled by a ditch that runs below the southwest part of the castle toward the Rhine. These engineered waterworks show deliberate control of a nearby supply to serve the castle and its immediate needs.

The oldest masonry cluster is concentrated in the southwest sector. There the ground plan of an octagonal great hall can still be traced, and this sector also contained a residential tower, or keep, plus a smaller building used for economy or stabling. In a later building phase a substantial shield wall nearly three metres thick was added on the northwest side and provided a timber-walk battlement on top. That later wall was narrower than the faces of the octagon, producing a shallow interior recess along the old hall wall.

Measured lengths of surviving fabric indicate a complex of considerable extent. The long northwest-facing wall of the old hall together with the later fortress wall runs about 95 metres according to older measurements, while the later shield wall alone has been measured at roughly 70 metres. Newer interpretations allow for an original extension north to the plateau, which would give a total linear length close to 140 metres. On the southwest face a sloping wall survives to about 17 metres in length.

The southeast sector preserves the route of the original curtain to the former main gate. That southeast wall runs roughly 35 metres to the gate position, then turns at about a right angle outward toward the rock edge along a wall of about ten metres, ending in a projecting horseshoe-shaped round tower whose diameter is estimated at ten to fifteen metres and which once intruded into the courtyard. From that projecting tower the east-side wall follows the rock edge northeast for about 50 metres and joins the northeast face, which measures around 30 metres at its ends.

Present access to the ruin is through a vaulted gateway set into the northwest wall, with an internal opening about 3.6 metres high and 2.1 metres wide; the historical authenticity of that passage is debated in the literature. Older drawings indicate additional entrances, and a contested gate on the northeast may originally have been crossed by a drawbridge spanning a defensive ditch.

Inside the defences a central courtyard approximately 45 by 29 metres sits between the two castle cores, and rubble mounds across that area mark the locations of former auxiliary buildings. Numerous rafter holes in the inner face of the northwest wall show where a wooden battlement and attached timber houses once stood, and some masonry in the later northern sector reveals a probable tower footprint of about 13 by 10 metres with an adjoining masonry residence of roughly 16 by 10 metres attributed to a later construction phase. Other walls in the older great hall zone are comparatively slim in places, about 1.8 metres thick.

Condition varies across the site. The northwest and northeast walls, conserved in the late nineteenth century, remain relatively tall and solid, with wall thicknesses over three metres and local heights up to about seven metres, although the north wall of the great hall is not intact. Large parts of the eastern southeast wall have been removed or quarried away, and much of the interior is overgrown, with the remaining mortar in the great hall described as brittle and in need of conservation. The chapel dedicated to Saint Joseph, marked above its door by a carved stone dated 1685, survives as the only fully preserved building; it was plundered in 1797 and renovated in 1949.