Campo di Marte is the Florence nobody photographs and Florentines actually live in — a calm early-twentieth-century grid built around a stadium that happens to be one of the great works of modern engineering. Four minutes by train from the duomo, it runs at a completely different speed, and Sunday is when that speed is best felt.
Start at Firenze Campo di Marte station, Mazzoni's travertine rationalist box, and walk straight to the Stadio Artemio Franchi. Pier Luigi Nervi built it in 1932, and the thing to see is the back: cantilevered helical staircases spiralling down in bare concrete, and the slender Marathon Tower — engineering that became sculpture without trying. On a non-match day you read it from the street, looking up.
Then let the grid take over. The villini with their gardens, Piazza delle Cure with its market and unhurried bars, the willow-lined Mugnone stream where the streets meet some air. Finish on the Campo di Marte parade ground itself, the field that named the quarter, wide-open in a city with no room. The train back into the centre is four minutes; you'll have had Florence's day off.