I second the Colonia suggestion .. a really neat all day trip. However be aware of the ferry! The same company runs two ferries (and I think it is the same one you book the tours of Colonia thru). One is a ferry that takes upwards of 2 hours to get there. The other is a 'high speed' hydrofoil ferry that does the trip in under half the time (and has a surcharge). The 'normal' ferry is great since you go out on deck and enjoy the ride. The 'speed' ferry has no deck space and basically airline seats (maybe 40 abreast) in the cabin and minimal way of looking out (there also is a 'premium' section tho not sure what they get extra).

I took the slow boat in the morning (LOVED it) to connect to the tour and then the fast boat at night (it got me back).

The hotel suggest I book a 'hotel car' from the hotel to pier (very early morning departure) and for the return (a zoo of people trying to get cabs and meet people). It worked out well tho probably was more $$ than a cab .. I did feel much safer!

Also, consider a Gaucho BBQ day trip. While yes it is touristy .. I really enjoyed it (it was on my final day 9am - 6pm and then left for airport at 7pm for flight back to US). There may be several places that run this .. but the one I went to was great. You get to ride a horse or in a horse cart before . then served a great dinner and later watch the Gaucho's show off their horse skills.

Two companies (at least) run the tours. One is a large company that uses full size commercial buses. The other is a small company that uses like 15 pax mini-vans. I went with the small company and LOVED it as it was much more comfortable of a group and less a 'tour'. The ride is 2+ hours from the city each way but going out it is interesting and they make a stop or two and get to the ranch earlier so you can explore the house and grounds .. heading back I dozed (thanks to the wine) and they went nonstop.

I really LOVED EZE ... the Evita Balcony was less impressive than I expected but I really enjoyed the whole trip.