When the morning ferry from Buenos Aires arrives in Colonia del Sacramento, crossing the Rio de la Plata and international borders, it offloads hundreds of daytrippers who make the 1-hour trip mainly to visit the Barrio Historico (Old Town), a UNESCO World Heritage Site.
Cobblestone streets and original buildings from the Portuguese colonisation era characterise this part of town, where you can easily stroll for a couple of hours before continuing your discovery in one of the many museums located in the Barrio.
You can also climb up the narrow staircases of the lighthouse and have a better and wider view of Colonia and the coastline.
A visit after sunset (the sunsets in Colonia are amazing!) will be the opportunity to enjoy the historic district under artificial light, which gives a magic touch to the area. Then sit and have a meal in one of the many small restaurants, tasting some amazing seafood or steaks :-).