One of the excursions you can make a nice sunny day from the city of Buenos Aires is known Colonia del Sacramento, in neighboring Uruguay. Cologne is on the Rio de la Plata, 177 kilometers from Montevideo, and can be reached by air, land or sea. But being in Buenos Aires is the best ride across the River.
Since Argentina’s capital ferries depart every day to make the crossing in three hours away. There are other options faster, of course, from Puerto Madero is a boat that takes only 45 minutes from the Delta del Tigre other boats also come to Cologne, but combined with a bus. The best option is the ferry, take it early in the morning to arrive early, spend the day in the village and come back when evening falls. The company responsible for transport by ferry between Buenos Aires and Colonia is Buquebus. The terminal is in Puerto Madero and have the 3 hour ferry and some fast ships which take about 50 minutes. Slow ships are the most used by tourists because you can make the trip part of the ride.
They also have wine so you can drive a car. Tickets can be purchased at various points in the city, in the Recoleta area, in downtown Buenos Aires or in Retiro Bus Terminal City. Another carrier is Cologne Express. In this case the ships depart from the River Terminal. There is also the company Seacat Colonia, very modern and fast. You see you have many options but my advice is that if you make a beautiful sunny day parts with the ferry in the morning, breakfast on board, deck and after walking around all day passes centenary people. The return in the evening you can admire the lights of Buenos Aires.