If they like to walk,
1) take the Av de Mayo form Plaza de Mayo to Congreso. Lots of spanish architecture and european vibe, plus you have lots of traditionals caffes. Its touristy though.
2) if they still want to walk, I ll go from the Facultad de Derecho up to the Jardin japones, all by Figueroa Alcorta and Libertador: you have ATC, the Palacio Errazuriz, now Museo Nacional de Arte Decorativo, the Malba, you can get in and go over Palermo Chico, the Paseo Alcorta mall, and finally the japanese gardens. A little long maybe.