There are three beautiful quarry lakes on the outskirts of Colonia, two pretty close and one almost 20 km away. Don't go swimming in them, but they're lovely to look at.
For a nominal fee you can go up to the top of the lighthouse (faro) and see most of the city and look out over the city and Rio de la Plata. On a clear day probably even Buenos Aires is visible. The lighthouse was built in 1857 and it is 26.92 m high with 118 steps. Its light is not white but red.
Plaza de Toros
Outside of the city is Uruguay's only bullfighting ring that is almost "unused". It was finished in 1910 with room for 8,000 spectators, but bullfighting was banned by law in the country two years later. The ring is now abandoned to total disrepair and fenced off for visitors' safety.
Casa del Virrey
Reconstructed somewhat on the ruins of the original building. Don't miss the whale skeleton on display just to the west of it!
The gate of the city with its draw bridge. Next to it are the ruins of the city walls.
Probably Colonia's most famous street and the view along the street towards the main square is featured on many tourist related publications of the town. The name of the street translates to "the street of sighs". There are two stories of how the street got its name: either because the houses along it used to be brothels, or because prisoners were brought along it before being put to death.
Goes along the seashore with a beautiful white handrail all the way.