Just a three hour ferry ride from Buenos Aires is Uruguay. You can choose between arriving in Colonia del Sacramento or the capital city, Montevideo. We took the ferry to Colonia, stayed there a couple of days and then went by bus up to Montevideo from were we took the ferry back to BA. Immigration and all exit & entry stamps were taken care off right in the ferry terminal at the port.
Montevideo is a sprawling metropolis and the capital city of Uruguay. It's smaller than Buenos Aires but still as lively and chaotic at times. Food-wise it's also quite similar to what you would find in Argentina: steaks and empanadas are on most restaurants' menus. Even the accent here bears some similarity to Argentinian Spanish even though I found Uruguayans slightly easier to understand.
Colonia is a beautifully preserved colonial town. Founded by the Portuguese in the late 17th century right on the edge of the Rio de la Plata it eventually became part of Spanish-speaking Uruguay. Today its historical quarter is a UNESCO World Heritage Site.
Funny story: in the tourist information office in Colonia we were given a small map outlining some of the town's sights. Somebody must have googled "Colonia" and copied the first image that came up... On the reverse of the map there was a picture of the Dome in Cologne/Germany :D
Scroll down for some impressions of Montevideo & Colonia!
Colonia del Sacramento