A short train ride and a great day trip from BA is the small town of Tigre, at the Rio de la Plata river delta.
Popular with rowers for good reason, Tigre is home to several rowing clubs, each with their own unique paddle design.
All along the waterways are these little cottages and houses...most of which are vacation homes for those who want to get away from the hustle and bustle of BA. Tigre is VERY laid back...especially in the backwaters in the delta.
I took a boat tour back into the delta...its a good deal and highly recommended, however the shorter ones don't get back to the truly wild parts of the delta, which are supposed to be beautiful. The shorter tours are nice to just relax (if you like boat rides that is) and enjoy the scenery of the populated parts near town. This is one of many old hulking shells of old ships long ago abandoned to the elements.
As mentioned above, I'd highly recommend a trip out to Tigre for some relaxation, fresh air, and to get away from the city for a bit.