Catania does not introduce itself well. It is built almost entirely out of the mountain that keeps threatening it - black lava kerbs, black church steps, black cobbles that turn to mirrors in the rain - and it has a working port city's indifference to whether you are charmed. Arrive for one rushed day and you will leave calling it grubby. Give it three nights and it turns into an unusually practical base for eastern Sicily: a real market, a volcano on a public bus route, an airport fifteen minutes from the cathedral, and trains running up and down the coast from a single station.
Three nights is the honest number. Two are enough if you intend to skip Etna, and skipping Etna is the one decision here that travellers tend to regret. Four earns you a coastal day trip without hurrying anything. Beyond that you are no longer visiting Catania, you are using it as a hotel for the rest of Sicily - a perfectly good plan, but a different article.
The two clocks that decide your order
Most cities let you shuffle the days around. Catania has two fixed points, and almost every scheduling mistake here comes from ignoring one of them.
The first is the fish market. La Pescheria, in the sunken square you reach by the steps beside the Amenano fountain at the edge of Piazza del Duomo, trades Monday to Saturday from around seven in the morning until the early afternoon, and it is at full volume roughly between half past seven and ten. Arrive at noon and you get wet stone and the smell. Arrive on a Sunday and you get nothing at all. A market morning cannot be your Sunday.
The second is the mountain. Public transport up Etna is not frequent: for most of the year there is a single scheduled morning departure from the square in front of Catania Centrale to Rifugio Sapienza, typically leaving around a quarter past eight and starting back down in the late afternoon. Miss it and your options collapse to a private tour or a hire car. That bus does not wait, does not care that your flight landed at one in the morning, and will not refund you for cloud.
So: put Etna on a full middle day, never on an arrival or a departure day. Put the market on a weekday morning. And if the forecast hands you exactly one clear day, spend it on the volcano and move the city around it - the Baroque is still standing in the rain, whereas the summit simply is not visible.
Day one: arrive, then walk the black city downhill
From Fontanarossa airport the Alibus runs into town in about a quarter of an hour, from very early until after midnight, for around EUR 4, and the ticket is generally valid across the city bus and metro network for about ninety minutes afterwards. A taxi is quicker and costs several times as much.
Stay inside the rectangle between Via Etnea, Piazza Università and the Duomo, or just west of it in Antico Corso, the university quarter, which is quieter and cheaper without being remote. The alleys of old San Berillo immediately north of the central station have been partly reclaimed by bars and murals but are still worth avoiding after dark, and nothing you need is in them.
Then do the walk that makes sense of the map, downhill, in the last two hours of light. Begin at Villa Bellini, the terraced public garden on Via Etnea, which on a clear evening frames the volcano at the head of the street - the view that explains the city's whole personality. Walk south. At Piazza Stesicoro the Roman amphitheatre sits in a pit several metres below the traffic, which tells you how much lava and rubble the modern city stands on. Turn off into Via Crociferi, a short uphill stack of church facades from the rebuild that followed the 1693 earthquake, and the reason Catania sits inside the UNESCO listing for the late Baroque towns of the Val di Noto.
Finish in Piazza del Duomo at the elephant. The lava-stone elephant carrying an Egyptian obelisk - u Liotru, to everyone here - is the city's emblem and its meeting point. Then eat. The lane of Santa Filomena, a couple of minutes off Via Etnea, is wall-to-wall tables, and FUD Bottega Sicula there does Sicilian ingredients in street-food form for people too tired to think. For a proper first dinner, Me Cumpari Turiddu, in the streets east of Via Etnea, appears among the Michelin guide's Bib Gourmand addresses in the city and serves the local canon; expect to pay roughly EUR 40 to 55 a head with wine. Order pasta alla Norma at least once - aubergine, tomato, salted ricotta - named after the opera by Vincenzo Bellini, who was born a few streets away.