The AP showing some skepticism:

Sanford told The State he was alone on the trip to Argentina. He declined to give any additional details about what he did other than to say he drove along the coastline.

Trying to make such a drive could frustrate a weekend visitor to Argentina. In Buenos Aires, the Avenida Costanera is the only coastal road, and it's less than two miles long. Reaching coastal resorts to the south requires a drive of nearly four hours on an inland highway with views of endless cattle ranches. To the north is a river delta of islands reached only by boat.

TPM Reader GK concurs:

Know that the "coastline" in BA is completely featureless and incredibly boring -- it's on a slow-moving, broad river. When residents of BA "go to the beach" they drive many hours away to Mar del Plata, which is on the Atlantic coast (or they hop on a boat to Montevideo, Uruguay.) But right now it's in the low 50's during the day and the mid 30's at night on the coast.