Colonia del Sacramento — if you have heard that the clocks stopped ticking in Uruguay, then this is definetly the case in Colonia del Sacramento. Just a 90-minute fairy ride from Buenos Aires, this is the perfect daytrip. People are really chilled here and you can spend your half day wandering through the streets. The city has a long history though and is even declared as a UNESCO World Heritage Site.
Strategically located at the Rio de la Plata, it was a quite important city for both the Spanish and Portuguese. So they started fighting for it. For nearly 150 years the control has shifted every couple of years between these two. Since 1828 it finally got under the flag of Uruguay.
You will find many museums, old cars and cafes to fill your time until the fairy leaves back to BA.