Zwing Uri, Castle ruin near Amsteg in Silenen, Switzerland.

Zwing Uri is a castle ruin perched on a hilltop in the Reuss valley near Silenen in central Switzerland. The remains show the foundations of a defensive tower and sections of walls from an unfinished fortification project.

The site on the Flüeli hill was settled in the Middle Bronze Age around 1500 BC, and by 1150 a farmstead with three buildings stood there. In the first half of the 13th century the dwelling was replaced by a residential tower about 10 m square. Around 1310–1320 a ring wall and neck ditch were begun but abandoned after roughly six weeks of work, and the castle was given up around 1350.

The ruins show how medieval fortifications controlled mountain passes and valleys in central Switzerland. This location was strategically important for the trade routes crossing through the Alps.

The site can be reached by several hiking trails, with the main route starting from Amsteg. Wear sturdy shoes and bring water, as parts of the climb are steep.

The hill was already settled in the Middle Bronze Age, around 1500 BC, long before the medieval tower. Excavations in 1978 and 1989 uncovered this earlier phase. Between the ruin and the railway line, the hill also housed the federal council bunker A 8760 / K8 Brindlistollen, now an underground data centre.