This behemoth of a building spans four tram stops and stretches over half a mile long. But its size isn’t nearly as impressive as its history, as this building was a stronghold for anti-fascists during the 1934 Austrian Civil War.

Karl Marx-Hof was completed in 1930 by architect Karl Ehn, a protege of the famous Otto Wagner, whose socialist style has had a lasting impact on Vienna’s architecture. The giant building took three years to finish.

The building was created to provide low-cost housing for the working class. Its residents were community-oriented and engaged in communal activities. Kitchens, laundries, and even bathrooms were all communal, requiring cooperation among residents. There was even a kindergarten on site.

Karl Marx-Hof also served as a fortress during the Austrian Civil War, which saw Nationalist and Marxist forces clash. Though it was mainly workers and their families—many who were unarmed— barricaded within the building, that didn’t stop the fascist Austrian army and Heimwehr from attacking the complex. The residents were forced to surrender after the building endured heavy fire.

Though the communal facilities are now split among individual apartments, Karl Marx-Hof is still a magnificent example of Socialist Utopian architecture. If you’d like to sneak a peek at the building’s past, you can pop into one of its old laundry facilities, which now holds a museum full of information and exhibits about Hof in its heyday.