Mauthausen and its sub-labor camp Gusen, combined to form the Mauthausen-Gusen Nazi concentration camp. 

View of the Mauthausen concentration camp. This photograph was taken after the liberation of the camp. Austria, May 5-30, 1945.
 

The camp were located near the  villages of Mauthausen and Gusen in Upper Austria, roughly twenty kilometers east
of the city of Linz.
 

Interior view of a gas chamber the Mauthausen concentration camp,
Jul 16, 1945.

View of the main gate to the Mauthausen concentration camp,
May-Jun 1945.

View of a mass grave dug by Austrian civilians to bury former inmates in the Mauthausen concentration camp,
May 5-15, 1945.
 

Apart from the four main
sub-camps at Mauthausen and nearby Gusen, more
 than fifty subcamps,
located throughout Austria
and southern Germany.
Many of the inmates were
used for slave labor.

Women and children survivors sit on the floor of a barracks in the newly liberated Gunskirchen concentration camp, May 6-7, 1945.
 

The two main camps, Mauthausen and Gusen I, were also the only two camps in the whole of Europe to be labeled as "Grade III" camps, which meant that they were intended to be the toughest camps for the "Incorrigible Political Enemies of the Reich. Unlike many other concentration camps, intended for all categories of prisoners, Mauthausen was mostly used for extermination through labor of the intelligentsia.