Puerto Madero is a modern development on the old wharfs of Buenos Aires. It is home to the fantastic Fortabat private art collection as well as the very trendy Faena hotel. Many traditional restaurants also have branches there. The Costanera Sur nature reserve is on the east side of Puerto Madero (http://en.wikipedia.org/wiki/Costanera_Sur_Ecological_Reserve). It is perfect for bird watchers and leisurely walks with great view os the city.