The Patras Carnival is the largest in Greece and ranks among the biggest in Europe, drawing hundreds of thousands of visitors over the weeks before Lent. It begins in mid-January and builds to a climax in the final weekend before Clean Monday (the start of Orthodox Lent), with the Grand Parade — a procession of enormous satirical floats built over months by competing groups — as the centrepiece event. The floats are large enough to require cranes and carry dozens of costumed participants; the best ones are genuine works of public art as well as political commentary.
The carnival tradition in Patras goes back to the early 19th century and has the depth that comes from long practice: there are children's parades, masquerade balls at the Apollon Theatre, treasure hunts through the city, and a general weeks-long atmosphere of celebratory chaos. The Saturday night before Clean Monday is the peak, with the Grand Parade running through the main streets and Georgiou Square filling to capacity. If you're in the Peloponnese in February, adjusting your itinerary to include the carnival final weekend is one of the better decisions you can make. Book accommodation months ahead for the Grand Parade weekend.