Achalm, Mountain peak in Reutlingen, Germany.

The Achalm is a 706.5-metre-high outlier of the Swabian Jura on the edge of Reutlingen, its cone made of Brown and White Jurassic sedimentary rock. On the summit stand sparse foundation remains of the medieval Achalm Castle and a viewing tower built in 1838 on the base of the former keep. The tower looks over Reutlingen, Eningen, Pfullingen, the Albtrauf and, on clear days, as far as the Hornisgrinde in the Black Forest.

Counts Egino and Rudolf had a castle built on the summit in the 11th century; only a few wall remains survive. It fell into decay in the 15th century, though some buildings were still lived in until the 17th. In May 1645 the Pfullingen administrator Andreas Hildebrand demolished it to prevent capture, and after the Peace of Westphalia the walls were quarried for town houses.

The name Achalm probably comes from an Indo-European root meaning "sharp, cliff". A folk etymology ties it to the dying words of Count Egino, who could only say "Ach Allm..." instead of "Ach Allmächtiger!". Ludwig Uhland used this in his ballad "Die Schlacht bei Reutlingen".

Several marked trails lead to the summit from different starting points around Reutlingen, each offering varying levels of difficulty for different hikers. Wear sturdy shoes and be ready for changing weather conditions at higher elevation.

The viewing tower on the summit was built in 1838 on the foundation walls of the medieval bergfried for King Wilhelm I of Württemberg. When it was restored in 1932, all 280,000 kilograms of building material were carried up the mountain by hand, and the work took about 5,400 man-days.