Answer
Rambla Montevideo stretches along the coast for about two dozen kilometers and connects different areas of the city. This is not one short tourist street, but a sequence of sections with beaches, public spaces, monuments, parks and residential areas. The specific length is indicated differently depending on the boundaries of the route.
You do not need to walk the entire waterfront on your first visit. Choose a section near Parque Rodó, Pocitos, Punta Carretas, Buceo or Malvín depending on your accommodation and interests. For travel between distant points, a bus or bicycle is more convenient; take the wind into account.
The Rambla is exposed to sun and weather: bring water, sun protection and a light windbreaker. Before swimming, check the flags and conditions at the specific beach, as a waterfront promenade does not mean that water conditions are the same along its entire length.