Colonia is a town across the river from Buenos Aires in Uruguay. Founded in 1680, it’s easily visited as a day trip from BA via ferry. Most folks just go to check out the old city for a day, and to use the ATMs to get U.S. dollars to take back to Argentina to change for pesos, or to renew their tourist visas. On that note, if you’re making the trip just to change dollars, try to get off the boat as quickly as possible and head down the main drag hitting ATMs, as many will run out of cash as other people with the same idea descend on the limited number of banks. The old city is very expensive given the tourist population, so I recommend heading a bit inland if you want to eat while you’re there.
It’s easy enough to get to Colonia from BA. Buquebus, ColoniaExpress, and Seacat all offer ferry service. ColoniaExpress is the cheapest. Your best bet is to head to one of their locations in BA, the most convenient of which is at Av. Cordoba 753. They have deals for there-and-back single day tickets for around US$45 round trip, and the boat ride is an hour long. All the ferries leave from the Buquebus Terminal at the north end of Puerto Madero.
I found 8 hours in Colonia to be plenty (ferry at 2pm from BA with 10pm return). The ferry ride is nice and relaxing, and once there you can quickly check off the main attractions such as the view from the local lighthouse and the small beaches. It’s not a bad place to chill out away from the bustle of Buenos Aires for a day, walk the quaint cobblestone streets and grab a few coffees. The restaurant El Torreón has a great roof terrace to watch the sunset from, although it is extremely, extremely overpriced.
A better option for sunset is to hit the small wine shop called Buen Suspiro at Calle De Los Suspiros 90 (it’s down in a classy looking stone basement). The wine here is fantastic and cheap, and the sunsets in Colonia are gorgeous, so having some vino on the beach in the evening turned out to be my favorite part of the trip.
Overall, if you’re in BA for a while Colonia is a fun day trip, but in my opinion Tigre is a much more fun destination if you’re looking for a convenient day (or more) out of the city.