If you are coming to Montevideo for its beaches, there are plenty along the shores of the Rio de la Plata. One of my favorite city beaches is Pocito Beach – it’s a crescent shaped bay with a long stretch of sand only a short ride from downtown and with plenty of shops and restaurants along the Rambla, the beach road, right along it!
While a city beach won’t give you the Robinson Crusoe feeling of a tropical island, it does have the convenience of all a big city has to offer just steps from the beach and Playa de los Pocitos is a great example of this. It’s only 15 minutes from the city center, easy to reach by bus or taxi, and has a great neighborhood right behind it. There are plenty of cafes, bars, restaurants and shops that would be worth a trip even without the beach! It’s an upscale neighborhood and felt very safe. There are mid-rise apartment buildings all along the beach, so it always feels like a city beach! 
And the beach itself is just right for a short getaway: it’s a beautiful bay with a wide strip of soft, yellow sand. You can lay down on the sand to get a tan or participate in a game of volleyball – or just watch. There are all even cafes and shops right on the beach, so you’ll have all the amenities you’d need. It was busy on a weekday in the shoulder season, so I can imagine it being pretty packed on a high-season weekend day! It was a lively scene and fun to people-watch. There is a grassy area at the Eastern end of the beach you can also hang out. If you want to combine it with some sight seeing, the Naval Museum is at the Eastern end as well. And if you need a Facebook photo, you can take it from the big Montevideo sign overlooking the beach – hundreds of visitors do everyday.
I wouldn’t fly to Montevideo just for Pocito Beach, but it’s worth going for a relaxing day if you are visiting the city or for a quick getaway from Buenos Aires. If you are looking for peace and quiet, one of the beaches further out from the city would be better fit, for example the longer and emptier Carrasco Beach!