Neu-Schauenburg Castle, Medieval castle ruin in Frenkendorf, Switzerland

Neu-Schauenburg is a ruined hilltop castle on a rocky spur at 600 m above sea level west of Frenkendorf, next to the Schauenburgflue rock formation. Its irregular ring wall follows the edge of the spur and includes a gate area on the north-east side reached by a ramp from the west. The spur has two terraces: the lower western part held a residential wing, while the higher eastern part probably carried a keep, now replaced by a modern viewing pavilion.

The visible remains date from the 13th century, though pottery from the mid-12th century points to an earlier castle on the site. The Lords of Schauenburg, a branch of the Rheinfelden stewards, held it until the family died out in 1385. Damaged in the 1356 Basel earthquake, it was repaired while Alt-Schauenburg was abandoned, which is why this older castle bears the name "Neu" (still in use).

The name Neu-Schauenburg means "new" only because it stayed in use after Alt-Schauenburg was abandoned following the 1356 Basel earthquake, even though it is the older of the two castles. By 1480 Beguine lay sisters had occupied its towers and ran a cloistered house in the ruins until 1523. In 1691 mineral springs were found and a bath house was built near the ruins.

The castle sits at about 600 m above sea level on a rocky spur west of Frenkendorf, beside the Schauenburgflue rock formation. Access runs on a ramp from the west around the northern corner to the gate area on the northeast side; the gate section was heavily altered in modern times. The ground inside the ring wall is uneven and divided into two terraces, so sturdy footwear helps.

The Beguines did not simply move into empty ruins: by 1502 the castle passed to them while they were already running the nearby Schwesternhaus, and they held the towers until 1523. The site had been uninhabited and left to decay before they arrived.