On 15 July 1927 in Vienna 89 protesters were killed and more than 600 injured, along with 5 police fatalities, when rioters broke into the Palace of Justice.
https://en.wikipedia.org/wiki/July_Revolt_of_1927
They were outraged by the acquittal of nationalist paramilitary thugs who had murdered a WWI veteran and an 8-year-old boy after a demonstration in the town of Schattendorf at the end of January. The killers pleaded self-defense. (I suppose the two had weaponized their bicycles?)
Several political parties and guilds and trade unions in Austria had formed their own militias in the wake of WWI. The one these defendants belonged to was particularly Nazi-like.
Here's a clip from an article about Austrian politics in the '20s:
*On 30 January 1927 members of the Frontkämpfer militia opened fire on an unarmed and unsuspecting crowd of Social Democrats in an ambush attack in the small town of Schattendorf, killing two and wounding five others. The Frontkämpfer were a right-wing vigilante group of war veterans, originally founded by disgruntled officers but also recruiting among the enlisted. Their stated aims were "uniting all Aryan front-line fighters" ("Vereinigung aller arischen Frontkämpfer"), "nurturing the love for the homeland" ("Pflege der Liebe zur Heimat"), fighting leftists, and suppressing Jews.
Their membership numbered in the thousands; a rally in 1920 appears to have attracted some sixty thousand sympathizers. The group's main activity was assaulting Social Democrats and Communists and disrupting their meetings. In 1927, the group was in the process of being assimilated into the Nazi Party, a process that would be completed by 1929
Karl Popper, the philosopher, was living in Vienna at the time of the riots, and he later wrote in a memoir “I began to expect the worst: that the democratic bastions of Central Europe would fall, and that a totalitarian Germany would start another war.”
In 2007 a memorial plaque was unveiled at the Palace of Justice by then-President Heinz Fischer.
Vienna's huge museum of military history has display cases with examples of militia uniforms and some charred remains of documents burned in the riot, but it (surprise) nowadays emphasizes the elements of Austrian resistance to national socialism.
https://www.hgm.at/en/visit-our-museums/museum-of-military-history/exhibitions
The museum has plenty of cute t-shirts and toy stuffed animals for your family back home.
Where do you like to visit in Austria to see reminders of its violent past?