Uruguay and Argentina are only separated by Rio Plata, with travel between the two nations short and easy. Many guidebooks on Argentina recommend a few destinations in Uruguay to visit, one of them being Colonia del Sacramento.
While in Argentina, my friend helped me book my trip to Uruguay through its website. I was planning to be in Colonia del Sacramento only for the day. The website is rather easy to navigate - and provides an icon of the craft that you'll be riding (Buque Rapido or Direct). The icons were a mystery to me then - but if you carefully read the schedule, you'll learn that the smaller craft is a Rapido (approx 1hr trip) and that the larger craft is a Direct (approx 3 hr trip).
Considering that I was going to be there for less than a day and that the trip each way would be 1-3 hours, I had a bit of a sticker shot when I learned that pricing was at least 200 USD. Pricing depends on dates/times, class, flexibility and f you're riding a Buquebus Rapido or not. Because I was trying to be conscious of my spending, I ended up booking the Direct on the return trip.
On the morning of my trip, I checked in at the counter at the Buquebus terminal, located near Puerto Madero. Luckily for me, the representative behind the counter spoke English, and I quickly retrieved my boarding pass. You must go upstairs to go through immigration, where you will need to fill out the form and present your passport. The process is simplified as both representatives from Argentina and Uruguay are in the same room. Entry to Uruguay is stamped on your passport before you enter the waiting room instead of going through immigration on the other side of the river.
There are no assigned seats on the ferry. First class is in a separate room from economy - and staff is at the doorway to validate your boarding pass. After 15 minutes after the ferry departed, the duty free shop was in service. Also, available on board is a snack shop which served common continental pastries.
The ride to Uruguay was very relaxing and luckily the waves were calm as well. However, on the return trip (on the Direct), there was a rainstorm that endlessly rocked the boat, causing me to be ill for a majority of the 3-hour ride. If at all possible, book the Rapido to avoid cases like these!
Also, don't forget to save the remainder of the completed immigration You will need to provide this to the Argentine immigration officials in Uruguay in order to return.