Burg Loch, Cave castle ruin in Pinswang, Austria.

Burg Loch is a castle ruin built within a natural rock cave on the southern slope of Schwarzenberg mountain. The grotto provided a natural shelter for medieval stone structures and defensive walls that were constructed directly into the rock formation.

The castle was founded in the 13th century by the lords of Rettenberg-Hoheneck and first appeared in written records around 1265. It served as a fortified position in the mountain region for several hundred years after its establishment.

The name Loch, meaning hole or cave, appears in 1265 with the castle guard Conradus de Foramine (Loch). The cave itself is about 35 m wide and up to 12 m deep, closed off in the 13th century by a straight front wall. A wall section dated to the 14th century south of it may belong to a small gate barbican.

The ruins sit on a mountain slope and are visible from outside, but exploring requires caution on uneven terrain. Sturdy footwear is essential, and visitors should be careful as the structures are ancient and portions may be unstable.

The 1552 inventory of Ehrenberg castle lists 394 "Falkonenkugeln" (falconet balls) that were "found in the Loch". They probably stem from 1546, when the ruin was reportedly used once more as a fortification against the troops of the Schmalkaldic League crossing the border near Füssen.