Tre Sassi is one of the Austrian stronholds built in the northern part of Italy and is located on the Valparola Pass between Falzarego Pass and Val Badia.

The construction of the fortress started in 1897 by Austro-Hungarian army and was completed in 1901, and later, between 1910 and 1911 was upgraded. This fortress had to defend the occupied territories north of Cortina d'Ampezzo – at that time, under Austrian rule. The Italians were trying to get these territories back.

On July 5, 1915, the fortress has been hit hard by Italian from the Cinque Torri area.

Today, the restored building hosts the Great War Museum (Museo della Grande Guerra) and and exhibits weapons and equipment of soldiers who fought in the mountains of the Dolomites.

Great War Museum is part of the museum complex all'aperto Museo della Grande Guerra. In the same are, one can visit the Edelweiss tranches, the Goiginger Gallery, an Austro-Hungarian military cemetery and another one of the Alpenkorps - the German Alpine troops.