Fracstein Castle, Medieval castle ruins in Seewis im Prättigau, Switzerland.

Fracstein is a ruined cave castle built into an overhang on a cliff on the north side of a narrow point in the Prättigau valley, above the Landquart River. Only the palas remains: a three-story, 19-meter-long building with a high entrance on the east wall and a window seat in the third-floor living quarters. The rear wall is the natural rock overhang, and some medieval plaster with carvings survives inside.

Fracstein was probably built in the 11th or 12th century, perhaps for the Lords of Aspermont, and was extensively rebuilt in the 13th century. It first appears in records in 1338, when the Aspermont brothers sold it to Count Friedrich V von Toggenburg, who made Ulrich von Matsch his vogt. In 1344 the Matsch and Toggenburg families left it as a shared castle; in 1436 it passed fully to the Matsch, who sold it to the Habsburgs in 1466. The Habsburgs abandoned it and by 1570 it was a ruin.

The carvings are not on the main tower but in the medieval plaster on the east inner side of the third-floor living rooms, where they can still be made out if you know where to look. They date from around 1300 and show helmets and the coats of arms of local knightly families such as Aspermont, Belmont and Rhäzüns.

From the old cantonal road, a small passage through the retaining wall leads to the scree slope at the foot of the cliff. A narrow, steep path reaches the ruin in five minutes without difficulty.

A defensive wall called Letzi extends from the southeast corner down to the river and was part of the original fortification system. This wall shows that the castle was not isolated but formed part of a larger network designed to control the valley.