Piz Buin (Romansh pronunciation: [ˌpits buˈiːn] ⓘ) is a mountain in the Silvretta range of the Alps on the border between Austria and Switzerland.

As part of the main Silvretta ridge, the mountain marks the border between Austria and Switzerland or Vorarlberg and the canton of Grisons, which runs across the summit in a west-easterly direction.

These two glaciers, located on Austrian territory, form the source of the Ill, which flows north through the Ochsental valley to the Silvretta Reservoir in Vermunt on the Bielerhöhe.

Piz Buin, like its surrounding peaks, is made up of crystalline rock from the Silvretta, which consists mainly of gneiss.

The vegetation is sparse, as is generally the case in the higher regions of the Silvretta, and consists of rock and debris-dwelling plants of the nival stage.

An alternative to this route leads from the Wiesbadener Hütte or directly from the Bieler Höhe to the Ochsentaler Glacier and over this to the Buinlücke.

This should be taken into account when planning a tour, especially in unfavorable weather conditions such as prolonged/heavy rainfall and prolonged heat with strong sunlight.

The endangered area of the normal route should therefore be crossed quickly and individually with the greatest possible distance to the foot of the Kleiner Piz Buin in order to minimize the risks.

Their original plan was to reach the Wiesbadener Grätle from the Bielerhöhe from the east, cross it and climb to the Buinlücke (3054m) via the gently sloping upper part of the ice stream, now called the Ochsentaler Glacier.

The route continued along the northern foot of the smaller Piz Buin to the saddle south of the Signalhorn, the "Fuorcla dal Cunfin", and from there through the Swiss Val Tuoi to Klosters.

At the time of the first ascents, both glaciers joined below the Grüne Kuppe (2579 m) in front of the Wiesbadener Grätli to the north, forming a medial moraine.

[5][6] In the summer of 2012, a new summit cross was flown to the mountain on behalf of the ÖAV, after the previous one, believed to date from the 1950s, had weathered and become misaligned.