Altfinstermünz, Medieval castle in Nauders, Austria

Altfinstermünz is a medieval castle in Nauders, Austria, built on a rocky ridge between steep cliffs above the deep gorge of the Inn River. The complex spans multiple levels with living quarters, watchtowers, and storage areas constructed directly into the rock face.

The fortress was established in the 11th century as a customs checkpoint monitoring trade through this Alpine pass between what is now Austria and Switzerland. Over the following centuries it was enlarged and reinforced as the crossing grew in importance.

The name Finstermünz likely derives from the Latin Fines intra montes, or from the Indo-European mintsja, "overhanging rock"; the site was first recorded in 1159 as "Vinestana silva". Tolls were collected here from around 1300, with the oldest surviving tariffs dating from 1534. The chapel of Mariä Himmelfahrt, built and consecrated in 1605, stands beside the gate tower.

The wooden bridge over the Inn, renewed in 1845 and reopened to pedestrians in 1999, is covered on the Austrian side and open on the Swiss side. The site lies at the foot of the Finstermünz Pass, where the old Reschen road met the river until 1854; the modern Hochfinstermünz road runs higher up. The buildings have been renovated since 2001 by the Verein Altfinstermünz.

The bridge tower of 1472 stands mid-river on a wooden bridge that is roofed on the Austrian side and open on the Swiss side. The five-storey residential and defensive tower has a machicolation projecting over the road, and a wall with a parapet walk runs to the rock slope.