The destination of my first trip to South America, Buenos Aires feels like a European (even Italian) city that was flourishing at the dawn of the 20th century.

The archbishop of Buenos Aires was elected Pope Francis just before my visit.
The Argentine Congress was designed by Vittorio Meano in heavy Italian classical style, and was completed in 1906.
Palacio Barolo, one of Buenos Aires' many art nouveau buildings (although in this case you might call it stile Liberty), was built by Italian immigrants with levels reflecting the structure of Dante's Divine Comedy - a sort of modern sacred geometry. It is said that the building was intended to serve as a repository for Dante's remains, should the tomb in Ravenna be damaged in war. The building's tower ("heaven") is crowned with a searchlight powerful enough to be seen across the River Plate in Montevideo, where a similar tower stands (Palacio Salvo).
The cemetery of La Recoleta has an amazing collection of monuments in a wide variety of architectural styles, including those we do not normally associate with death in Europe, such as art nouveau and art deco.

Not far from the capital, along a British railway (via English settlements such as City Bell), one can find the planned city of La Plata.

The cathedral of La Plata confidently synthesises French and German styles (with the emphasis on the French), reflecting the ancestry of its architects. However, the use of red brick reminds one of Uppsala (itself a French design), and the crossing lantern is perhaps of Spanish (even Moorish) inspiration. Overall, the cathedral one of the largest gothic structures in South America.

Colonia Del Sacramento is a small town in Uruguay (across the river from Buenos Aires), which preserves many of its original colonial buildings.