Colonia is pleasant year-round. The southern summer (December to March) is warm and sunny, with temperatures in the mid-20s Celsius. These months are also the busiest, with Argentine holiday-makers and day-trippers from Buenos Aires filling the historic quarter on weekends and during the January–February school holidays. If you want a quieter experience of the cobblestone streets, aim for the shoulder seasons.
Spring (September–November) and autumn (March–May) offer mild temperatures, fewer crowds, and the kind of soft light that makes the colonial streets look their best. Winter (June–August) is cool and sometimes rainy, but the town is at its quietest and most atmospheric; the cafes by the fire and the empty streets early on a grey morning have their own appeal.
The most important local event is the Fiesta de la Hispanidad in October, celebrating the town's founding. There are also various cultural events and a film festival that attract visitors in the spring months.