Sfax has little to interest the tourist and is really only worth visiting as a staging point on a longer journey.
Sfax-Thyna Airport has two flights per week to/from Paris CDG Aiport with Tunisair. You can also reach Sfax by internal flights with Sevenair from Djerba, Tozeur, Tunis or with a Libyan Air or Sevenair flight from Tripoli.
A highway connects Sfax to northern cities like Tunis and Sousse.
Train connections are available from the train station in the centre of Sfax to most major Tunisian cities.
The trains are NOT frequent, and slow. Sfax to Tunis is 4 hours by train, 3 hours by road for example, but much more comfortable!  Last train Sfax to Tunis is 18:20]]
Sfax has two bus stations. Soretras, which is the regional bus company, and may not offer air-con buses, is on Rue Commondant Bejaoui, a few blocks past the central market.
SNTRI Bus station, which offers long distance buses, may be marked incorrectly on some travel guide maps. It is not across from the regional bus station, but is roughly 400 m to the south, along a dusty road through an industrial area over the train tracks. It is best best to take a taxi there, especially in the summer (less than 2 TD from the Medina/Blvd Republique). The bus station is in the same building as the TunisAir office.
Sfax to Tunis by louage is 16 dinars, and you get driven by Stirling Moss talking on the phone the whole time steering with one hand, in a 9-seater minibus. The system looks chaotic, and but is actually quite efficient. You join queue at a tatty window at front, pay your money, get ticket, and then walk through the building. Outside are all the minibuses, and they tell you which is the next one to go. They cram your case in the back, and minibus leaves when full - usually within a few minutes. Beware there is a collection AFTER you sit down of 300 millimes for the tolls.
Maybe avoid in hot weather as Tunisians seem to hate using air-con.
Public transport is easily available in Sfax.
Taxis are economical, and getting around in the downtown area should cost less than 2 TND per ride. They also tend to automatically use the meter. For example, this would include from Bab Bhar (south of the Medina) to Sfax Jdiid (north of the Medina), or from the Railway station to Hotel Syphax.
Buses are rarely used by tourists, since they are irregular, slow and crowded. If you are going to a destination on one of the roads that radiate out of the city, a taxi might cost about 3.500 TND to kilometer 8, for example. A bus would only cost .510 TND. These buses depart from locations around the Medina (mostly to the north or to the east). The site www.ecfi-t.com has a useful map of bus routes, as well as other information about Sfax.
Transport between cities can be done by train or by louage. Trains go south to Gabes for the Ksour district or sites where Star Wars was filmed, or north to El Djem, Sousse or Tunis. Trains have 3 classes of travel: 2nd class, 1st class and Confort. The last is recommended, especially when the train is crowded, since the inspector will move passengers out of seats where they don't belong. The Confort class is a separate section within one of the 1st class coaches, the smaller section, with about 24 seats. (Often locals do not realise this, and will sit there until moved on by the inspector, or wiser souls.)
The Louage is a minibus of about 9 passengers. The Louage station is located beyond the western end of Avenue Bourguiba, about 1.5km from the railway station (and so is worth a taxi fare). The louage driver will wait until the 'bus is full, which may mean an hour or more at quiet times, or to infrequent destinations. A wait for a ride to Tunis, El Djem or Sousse should not take too long, but if you are in a hurry and there is only one or two seats left, offer to pay for an extra seat or two.
Bus transport between cities is also available.
Wander around the fascinating Medina (which has an easily mastered and logical layout) where life and business go on much as they have for years and where tourists, although welcome, are few and far between.
Ride to Kerkenna on the ferry, with 8 trips a day costing about 800 millimes each way. In Kerkenna, get a taxi to the Hotel Cercina where you can walk the beach, or sit on their patio and enjoy tea looking over the bay. Check the times of the ferry's return, and make sure you get a taxi back in time! From the Grand Hotel you an also walk the beach, with your destination, the old Bourj, visible in the distance. About 1.5km each way, so give yourselves time to enjoy it. The Roman ruins beside the Bourj are opened to public as well.
You can find a lot of shops in downtown area.
Budget accomodations include several hotels immediately inside the medina from the main gate (Bab Diwan), just off to the right. Of these, Hotel Besbes is considered as the least worst of these.