Avenida Internacional is the border itself: Uruguay on one side, Brazil on the other, with no river, fence, or checkpoint interrupting the street. You can cross countries mid-block, then notice the currency, language, and shop signs change around you. It is not grand, but it is one of the easiest places in South America to feel how arbitrary a border can be.
The avenue is lined with duty-free stores, exchange houses, and practical businesses aimed at shoppers from both countries. Come for a wander rather than a sight in the usual sense. Morning is calmer; late afternoons and holiday periods can feel like a retail scrum.