Ruine Schalberg, Castle ruin and archaeological site in Pfeffingen, Switzerland.

Ruine Schalberg is a two-part castle ruin about 100 metres long, with an upper castle and a lower castle to its northwest, on a rocky ridge above the narrowest point of the Aescher Klusertal at 444 metres. The upper castle's round tower, nearly 7 metres in outer diameter but only about 3 metres of clear interior width, is enclosed by walls up to 2 metres thick. The lower castle's extent is visible in terraced surfaces, and several buildings can be traced by their wall remains.

The Schaler family, a Basel noble lineage, built the castle in the late 13th century, later than their nearby Engenstein and Frohberg strongholds; Carl Roth suggests either Peter Schaler or his son Rudolf as builder. Around 1300 the family handed it to the Bishop of Basel and held it back as a fief. Damaged in the 1356 earthquake and repaired, it was abandoned shortly after 1400; the Schalers died out in 1437 and the castle passed to the Counts of Tierstein. It was last mentioned as a castle in 1452.

The resident branch of the Schaler family called itself "von Schalberg", giving the ruin its name. Since 1975 the site has been the traditional home ground of the Schalberg scout group from Basel, so visitors may meet scouts camping among the walls.

Wear sturdy shoes as the path is steep and rocky with uneven footing throughout. Bring a flashlight if you plan to explore the cave section, as it requires entering a dark chamber on the main route.

The Schalberghöhle, a cave on the climb to the ruin, was inhabited in the Stone Age. Limestone quarried from the two artificial neck ditches just below the castle was used to build Schalberg itself, so the defences and the masonry share the same rock.