Florence looks up at Fiesole, and Fiesole looks down on Florence — and the older town wins. It was a city when Florence was a river crossing, an Etruscan stronghold on the hill, and it still has the ruins and the long view to prove it. A short walk up top, all of it uphill, all of it worth it.
Under four kilometres, best on a clear afternoon. The Bus 7 climbs from the city and drops you in Piazza Mino da Fiesole — coffee first, then the Duomo di San Romolo, bare and ancient-feeling. Behind the square, the Roman theatre sits cut into the hillside, still hosting summer concerts after two thousand years.
Then the climb the town is shaped around: up Via San Francesco, stopping at the public terrace where Florence lies on the valley floor, the duomo shrunk to a thumbnail. At the top, the Convento di San Francesco on the old acropolis, with its silent cloister.
Come back down to Piazza Mino for the Bus 7 — or walk the old road down to Florence if you've the legs.