It was just three weeks ago that I went to Tigre and the river delta region, about an hour away from Buenos Aires. We went by train (see the tourist tips section below for more detail) along the coast. We could have gotten out and explored some of the stops along the way but chose not to because of timing and needing to be back for dinner at Casa Saltshaker that night. When we got to Tigre there were many commercial options for taking a hour to three hour tour of the region, water taxis to many of the islands and local restaurants and resorts on them, and service to Uruguay river resorts. There are also many pleasant restaurants overlooking the river and we opted to have lunch in one of them and then decide if we would take a boat ride. Right after lunch there was thunder and rain and we said, um, don't think it would be a good day to be on the water. We ended up going to the Puerto de Frutas instead. The old fruit wholesaling facility has been converted into shops, handicraft booths and food vendors. It was full of day tripping locals and was a fun but lightweight diversion. I enjoyed the Museum of Mate much more.
More on the mate museum (and mate) can be found here. Watch for other aspects of our day trip later as well as Casa Saltshaker and our Vietnamese meal in Argentina.
Buenos Aires Tourist Tip: To come (I need to find my notes): step by step how to get to the delta by train. This is easy (and inexpensive) to do yourself, you don't need to pay a tour company for an excursion.