region of Uruguay
The Northern Interior of Uruguay is a land of ranchers, cattle, and horses. Between the streams, hills, and hot springs of the sparsely populated departments of Artigas, Paysandú, Rivera, Salto, and Tacuarembó, life can feel a world away from Montevideo.
This is gaucho (South American cowboy) territory. Don't be surprised to see men in distinctive, old-fashioned clothes riding horses down city streets or beside the highway. Outside of the downtown areas of major cities, you'll see cows and horses grazing almost anywhere you go.
Regular buses are available from other parts of Uruguay, and there is also a bus to Salto from Concordia, Argentina. You can also take a bus to Santana do Livramento or Quaraí in Brazil and then walk across the border.
Uruguay has a good internal highway system that connects this region to southern Uruguay. You can also drive across the border from Brazil to Rivera, Artigas, or Bella Unión; or from Argentina to Paysandú or Salto.
Even though you can see the Argentinian city of Monte Caseros from Bella Unión, there's no bridge between the two cities, so drivers would have to go around and cross at Uruguaiana or Salto instead.
Well, on weekdays there are boats between Monte Caseros and Bella Unión, but other than that you're pretty much going to be driving or riding a bus.
This region is relatively sparsely populated and bus service may be infrequent. Some cities are connected by frequent buses on their way to or from Montevideo—for instance, you should have no trouble getting from Salto to Paysandú or from Tacuarembó to Rivera. But in other cases you might have to transfer or wait for a bus that only runs a couple times a week.
Cities on the Brazilian border have duty-free shops catering to visitors from across the border. The biggest selection seems to be in Rivera, and across the border in Santana do Livramento there are a bunch of cheap Brazilian shops too.