Plaza del Congreso is a major park and plaza in Buenos Aires in front of - you guessed it - the National Congress. The entire square is part of a 7.5-acre open space with three adjoining plazas.
The Kilometre Zero for all Argentine National Highways is marked here.
You can also see one of only 3 replicas of Rodin's The Thinker in the center of the plaza.
Fun fact: Avenida de Mayo joins the Congress and the Casa Rosada, joining two branches of the federal government. The symbolism is purposeful and is important in both protests and changes in power after Presidential elections (the new president is sworn in in Congress then takes Avenida de Mayo to the seat of executive power).