Ferries run frequently across the Río de la Plata between Buenos Aires and the Uruguayan cities of Colonia and Montevideo. Seacat or Colonia Express catamarans, which take an hour or less to Colonia and three hours to Montevideo, offer the best value. Full-price round-trip tickets cost around 1,000 and 1,250 pesos, respectively, but they often drop as low as 650 and 770 pesos if you book online (same-day return tickets are sometimes even less). Buquebus offers similar services on high-speed ferries, with round-trip tickets costing 1,350 pesos to Colonia and 1,550 pesos to Montevideo.
All three companies also sell packages that include bus tickets to Montevideo and Punta del Este direct from Colonia's ferry terminal. You can order tickets by phone or online.
Buquebus and Seacat leave from terminals at the northern end of Puerto Madero. The Colonia Express terminal is south of Puerto Madero on Avenida Pedro de Mendoza (the extension of Avenida Huergo) at 20 de Septiembre. It's best reached by taxi.
Buquebus. 11/4316–6500; www.buquebus.com.
Colonia Express. 11/4317–4100; www.coloniaexpress.com.
Seacat. 11/4314–5100; www.seacatcolonia.com.