Achalm Castle

The castle occupies the summit of the Achalm at 707.1 metres above sea level and was laid out so that the entire summit area became part of the fortification. The top is an elongated oval with a rocky projection to the southeast, and the plan divides into a lower ward and an upper ward, the latter forming the heart of the complex. The earliest fabric includes an encircling wall around the upper ward, and surviving evidence indicates that the main defensive tower was erected in the twelfth century while an eastern tower dates to the thirteenth.

Approach from the south follows the original castle route into a gateway courtyard bounded by a stout outer wall that still stands to a thickness of about 75 centimetres. Just before the second, largely ruined gate, a small side gate with corbelled lintel masonry opens outward. Beyond that gate lies a forecourt that was once enclosed by walls; the lower ward begins to the left of this forecourt and remnants of a curtain wall run in a polygonal line along the rocky margin of the summit. On the east side an unrestored section of eleventh‑century wall displays courses of small, layered ashlar blocks, visible in place today.

The upper ward is set roughly six metres above the forecourt and contains the principal structures of the castle. The main defensive tower, known as the bergfried or main tower, originally had a high entrance that appears to have been reached from an adjacent residential building by a connecting passage. During the deliberate demilitarisation of 1646 towers and stretches of wall were demolished and the cistern was filled in; the dwelling standing above the gate was burned later in that year, leaving the upper ward in a ruined state. Final demolition efforts in the mid‑seventeenth century further reduced the standing fabric.

A round tower now occupies the highest point where the medieval bergfried once stood. It is built of natural stone and measures approximately 7.20 by 7.20 metres at the base, rising about 14 metres from the original plinth. The lower portion of the tower, up to about 8.70 metres, retains medieval walling roughly 1.75 metres thick. The section above is of noticeably thinner construction and is faced internally with brick, reflecting a later rebuilding campaign that raised the tower to an overall height near 18 metres. A modern steel staircase runs up the interior wall faces to a covered exit at the viewing platform, which is fitted with an orientation panel and a flagpole. The rebuilt tower was repaired in 1932; masonry damage from an incident in 2017 briefly closed access but the structure has since been made accessible again.

The ruined hill is reached by a nearby parking area at the summit ridge and by marked footpaths. The long‑distance castle walking route along the Neckar‑Donau runs across the Achalm, passing the remains and linking the site with other regional heritage points.