This sumptuous 1915 building, mixing retail and office, was one of the city's tallest at 85m (279 ft.) when it opened. The ugly modern Calle Florida entrance, rebuilt in 1971 after a fire, makes it easy to overlook. Its back entrance on San Martín hints at its original glory. The shopping gallery has a mix of stores without distinction, but look around at the walls and decorations. The architecture is a mix of Art Nouveau, Gothic, Byzantine, and neoclassical -- all heavily ornamented -- and was the creation of the architect Francesco Gianotti who designed the now-closed Café del Molino next door to Congreso. Make sure to look at the ornate elevator banks. Much of the exquisite material came from Italy, having had to be created twice as the original shipment was destroyed on a boat fire. The building also houses the Piazzolla tango show. The Art Nouveau theater in which it sits was closed for nearly 40 years and was restored in the early 2000s, and it is the most beautiful of all the tango show palaces in Buenos Aires. Little Prince author Antoine de Saint-Exupéry lived in this building too. A gallery on the second level has photos from the early days of the building.