On the fast Buquebus ferry from BsAs to Montevideo. We did a package, ferry + hotel, and ended up in business class. This was way cool - lots of space and on the way back, free ice water, champagne, and cookies! The kids enjoyed their first first-class experience. This was one of the 2 coolest things about the trip.
Our first day in Montevideo was May Day, an international holiday and about everything was closed. So we walked around downtown and on the river front promenade. The old town is on a peninsula in the Rio de la Plata, so there's a very nice river-side walk, with many playgrounds, going kilometers out of town to the good beaches. We didn't walk quite that far, as there was an indoor pool waiting in our hotel and we needed to get back to swim.
On day 2, it was supposed to rain all day, so in the earlyAM we went swimming, and then took a tour of the Teatro Solis, built in the early 20th century for a private company but now the home of the national orchestra & theater, with very cheap tickets, about $6USD. The tour was neat, especially the acting interludes, when students from the national theater school interrupted the tour with drama, loosely based on the life of Delfina Agustini, an Uruguayan poet to who was tragically murdered by her ex-husband. I kid you not about the melodrama, both in her life and by the actors. Silas was rapt.
The theater itself was an Italianate U and came with more acting. The actress was in love with her balcony and spouted doggerel. It was hilarious, but for some reason, none of the folks in the English-language tour were laughing. Silas enjoyed her rhymes.
After the theater, we got very very wet walking to a market and the carnival museum. Then we went swimming again at the hotel (the second best thing about Montevideo), and out for dinner at another market, the MAM (Montevideo Agriculture Market), in a restored old market building near the national Legislature. The last morning before taking our boat back, we went to the huge Sunday morning street market. It was gigantic and full of fish, fruits and vegetables, tourist stuff, antiques, you name it. It was very interesting until I realized my wallet was stolen. That put a damper on things as we needed to call in about my credit cards, which Mike did while waiting for the ferry.
In sum, Montevideo has some sights, nothing earth-shattering and it's generally just a normal small capital city for a country of around 2 million people. I wouldn't recommend going there on a holiday when everyone leaves town, or carrying your wallet in your backpack. We went to Colonia del Sacramento last week with my mom, also in Uruguay, and I'd recommend that day trip/weekend first. It was a small town that still retained a lot of its interesting colonial center.