The town is more than 340 years old. It was founded in 1680 by Portuguese sailors, then taken over by Spanish settlers, and then Portuguese again, swapping back and forth many times over the years. Each group of settlers built houses in their own style, which is why the old town has such a mix - some streets feel Portuguese, others Spanish.
The most famous street is called the Calle de los Suspiros - the 'Street of Sighs'. It is a narrow, sloping cobbled lane that runs down to the river. The cobblestones are uneven, the houses lean towards each other, and a single oil-lamp lights it at night. Walking down it feels a bit like stepping into an old painting.
On a hill near the river stands the town's lighthouse. It was built in 1857 on top of the ruins of an old convent. You can climb the spiral staircase to the top for a view across the river that is so wide it looks like the sea. On a clear day you can sometimes see all the way to Argentina, on the other side.
Today, Colonia is a quiet place where children play on the cobbles, old cars are sometimes turned into flowerpots, and people sit out at evening with mate in hand. Most visitors arrive on a fast boat from Buenos Aires in Argentina, which takes about an hour across the R铆o de la Plata.