See: Cementerio de la Recoleta
The permanent residence of many of the country's great historical figures and families, Recoleta Cemetery is similar in its hauntingly beautiful state of decay to New Orleans' cities of the dead. Hunting for former first lady Evita Perón in four acres of incredibly ornate mausoleums is only mildly creepy on a sunny afternoon.

Other super-touristy must-sees: 
@CasaRosadaArgentina
#FloralisGenerica
#Obelisco