Critical Mass Brno was founded in May 2017 and takes place every first Wednesday every month. This event is organized by a citizens' initiative Brněnská Cykloguerilla (Bike Guerilla Brno).
Critical Mass in Brno is called "Zkouška sirén" (Siren test) after siren tests which are held in the Czech Republic every first Wednesday at noon.
Meeting point: Moravské náměstí / Moravian square, google maps
official website: http://criticalmassbrno.cz/