A 3min walk from the Catedral subte (metro) stop, you'll find Galleria Guemes. Built in 1915, Galería Güemes was the city’s first skyscraper. The 16-story building is now an average mall housed in one of the best art nouveau buildings in the world. It is said that the writer of The Little Prince, Antoine de Saint-Exupéry, once lived in an upstairs apartment in this building.
Sit in the cafe on the ground floor and look up at the glass dome ceiling. For 60 pesos, you can take an elevator to the 14th floor, then climb a spiral staircase to see views of the buildings in the Florida area and the Rio de Plata in the distance. The observation deck is open M-F from 9-12pm, and from 3pm – 5:30pm, but is closed on weekends. We popped into this building around 1pm, so we couldn't go to the observation deck, but we had already visited nearby Palacio Borolo, which is higher, anyway.