Some of the greatest concentrations of Beaux Arts and Art Nouveau buildings in the city are in this district. Meanwhile, because of its location and political affiliation, it has traditionally served as as a route for both grand parades and protest demonstrations. During our stay we were able to take in a ring side view of a huge LGBT pride parade in front of our hostel (see photo below) that, as it turns out, happened only days before presidential elections.
Though this has been an important area for sightseeing for many years, the whole neighborhood seems to have a run-down feeling to it. It can seem desolate at night, especially in the Congreso Plaza, which serves as a hangout for the homeless. It's a startling reminder of class distinction to see makeshift camps of those suffering abject poverty in the park immediately south of the state legislature.
There have been periodical waves of new businesses, however, and numerous hotels have opened in this area, as well as some significant cafes and restaurants such as 36 Billares (often featuring tango duos and trios) and La Americana.
An important feature of this neighborhood, hinting at the area's former glory, is the Cafe del Molino at the northwest corner of Rivadavia and Callao. An Art Nouveau masterpiece, it was the informal meeting place of politicians and the powerful until shutting its doors in the 90s.
Along the northside of Callao, you'll come across blocks of decaying marble and stucco neoclassical buildings that have an almost imperial sense and call to mind Buenos Aires's glory days and Argentina's desire to rise as a global power.
This is an important district to visit in that it serves as a reminder to how misleading the romanticizing of a place can be and the relationship the political class often has to the people it governs.