Slip into a kayak or take a cruise for the best views of this urban waterworld, a fast-growing city tucked into a bend of the Parana River about 186 miles northwest of Buenos Aires. Vegetation-cloaked islands with quiet campsites flank its waterfront, while the city center bustles with discos, theaters, pedestrian malls, restaurants and parks popular with cyclists. A national monument on the riverbank honors the city's historic role as the site where the Argentine flag first flew.