Sousse (سوسة Susa) is in Tunisia.
Sousse is one of the older cities in Tunisia possessing an authentic medina, which has been declared a UNESCO World Heritage Site. It is a popular tourist destination, particularly with Russian, Serbs, Croats, Britons, Germans and East Europeans. Located on the coast, it has good beaches and a clear turquoise sea.
Since Sousse is a city in a Muslim country, check the Muslim holidays before your visit. If you are able to celebrate the holidays with a local family, this will be a interesting experience. If you are not able to, you will find a lot of excursions, museums and shops closed on holidays.
The most convenient airport is Monastir which is to the south on the coast, 20 minutes away and frequently used by holiday charter flights. From this airport it is very easy to get to the town as there are frequent (every 20-30 minutes) trains (locally called "metro"), costing around 1DT one way. The train station is located 200 meters from the airport, just across the parking area. At the moment the newer airport called Enfida (located around 50km by road from Sousse) is much more popular than the one in Monastir. Unfortunately transportation is less convenient. You must wait for a local bus (roughly one every 90 minutes) or take a taxi to Enfida town where you can catch a louage. If you have a flight to Tunis, take the train or a louage. Both of them are in the center of town and cost about 9DT one way.
Sousse is on the main line from Tunis in the north down to Sfax and Monastir to the south. Because it is located in the centre of the railway network it is well placed to reach most of the rest of the network, even as far south as Gabes on the coast and Tozeur on the edge of the Sahara. Example fares from Tunis to Sousse are 12/10/6 dinars in Grand/1st/2nd class, although paying extra for first class doesn't guarantee you a seat if the service is busy. Tunisisan railways are mainly for goods traffic with passenger traffic taking something of a back seat so don't expect to find yourself rattling along at 100 mph; 50 to 60 mph is more likely and the standard of the rolling stock (carriages) can be poor. That said rail services are generally reliable and above all are very cheap, even for the top class (Grand Classe Confort). They can be an excellent way to get about the country, just don't expect Pullman style travel. The national railway company, the S.N.C.F.T. has a workable website that includes timetables and fares  although you will need some rudimentary French to navigate it as the English language option was "under construction" at the time of writing. As Sousse is relatively local to Tunis you should expect heavy use by local commuters and reserved seats may not actually be available. Wikipedia has an article on Tunisian railways  which includes a map showing network coverage.
Highway A1 connects Sousse with Tunis. A toll applies for using the highway. Additionally, Sousse is crossed by National Road 1 (RN1), connecting the city with the south of the country, and Libya. Roads are in very good condition. Additionally, a car ferry connects Sousse with Trapani in Italy once a week i the summer months. Please note that driving in Tunisia can be a very dangerous and harrowing experience, with drivers rarely observing even basic rules of the road, accidents being extremely frequent.
Buses (car) connect the city with most other parts of Tunisia. Additionally, there is a louage (shared-taxi) service covering the entire country. The far bus station (Gare Routiere) is located in some distance to the west of the Medina at the Souk El Ahad ("Sunday Market") - the City bus station is located next to the Medina in the town center). Prices are slightly lower than those of second class train tickets, but many buses do not have air conditioning.
Car ferries and express boats connect Sousse with Trapani (only in the summer months, once a week for cars and passengers) and Mazara del Vallo via Pantelleria 3 times a week, only for passengers. It takes up to 7-8 hours to Trapani and 5 hours to Mazara del Vallo. Private boats and yachts can use the marina at Port El Kantaoui (a resort about 12 km north of Sousse).
Taxi drivers in Sousse are mostly honest and will use the meter (starting at TND 0.500 daytime, TND 0.750 9PM-5AM), though some will try to charge you a high fixed fare. When entering the taxi, make sure the driver uses and restores the meter - gently gesturing them will usually work. If a driver refuses to use the meter, just leave the car and find another driver. Taxis are yellow, and have a taxi license sticker on the windshield.
Shared taxis (Collection taxis, Louages) are large cars or minibuses/people carriers which start their journey when they are full. Well used by the locals, expect to pay 10% of the price of a taxi. Shared taxis can take you further than regular taxis, connecting the city with most bigger towns in Tunisia. Shared taxis for destinations in the same or a closely adjacent city (eg. Hergla, Chott Mariem) are also yellow with a blue stripe on the middle of the taxi. Shared taxis between cities (far connections) are white with a red stripe. In Sousse, there are also white taxis with red, black, blue and yellow stripes serving destinations in the greater Sousse area (eg. Akouda, Hammam-Sousse, Kantaoui, Chott Mariem). They leave from the "Station Louage" which is best reached by normal taxi (see above).
Tuk-Tuk's and Mini-trains can get you a fun ride to Port El Kantaoui, which is about 12 km away. They are open, shared transports and start their journey when they're full (or almost). Expect to pay 2 dinars per journey at the first and 2,5 at the latter. Tuk-tuks are bright purple.
Horse-drawn carriages provide another option for a fun ride to Port El Kantaoui at no more than double the price of a taxi (if you bargain).
All of Sousse's sights are located within the labyrinthine medina in the heart of the city.
Don't expect to have language issues as merchants speak almost anything common (French, English, Italian, Spanish, German...) - you can mix all languages if you want. During Muslim holidays only part of the shops will be open.
Products to buy:
Two people can have a nice meal for around 10 dinars or less (depends on the place), but prices are generally low. For this you don't have to negotiate prices.
Dates are one of the biggest export products of Tunisia, try them fresh instead of the dried kind that are sold abroad.
Restaurant du Peuple serves traditional Tunisian dishes, such as grilled (very fresh) fish and meats, couscous, brik, ajja, pasta with seafood, Tunisian salads, mechouia and so on. Prices are extremely reasonable by European standards and the quality is high. The staff are also very pleasant and welcoming, being mainly women (family-run). It is located very near the main entrance to the medina, close to the bus station, but behind the ramparts just within the medina (I don't think there are any street signs but just walk along the inside of the ramparts, walking away from the shoreline, and you will see it after about 30 metres).
Restaurant Lido; excellent fish restaurant by the port, opposite the 'pirate' ships. TND 15 for a spiced and grilled fish fresh from the port, a reasonable TND 2.1 for a beer.
Hotel Medina, behind the Central Mosque, serves excellent meals for an average of TND15, has wine and serves as the local bar.
There are several good restaurants just north of the Medina (old town). One of them is La Caleche. Expect to pay around 20-40 TND for a meal. Alcohol is available.
Drinking tap water is generally not harmful - some people and almost all tourists prefer, though, to use the bottled water that you can find everywhere (very cheap, for around 0,200-0,400 TND for 1/2 liter, 0,300-0,650 for 1.5 liter). Non-carbonated (non-sparkling) water is the most popular, and is called "mineral water". Carbonated water is available as well, but you must specifically ask for water with gas (eau avec gaz) or Garci (the most popular brand).
Expect to find a Coke for around 0,800 to 1,5 TND (depends if in a supermarket or hotel).
The favorite beverage of the locals is tea, with many tea based specialties being available at the many cafes and restaurants around town. A favorite amongst locals is the au menthe (tea with mint leaves and sugar) and the aux ammandes (tea with crushed almonds and almond essence). Most locals will drink it while smoking from the chicha (the local name for a hookah). Expect to be offered tea while buying things of relatively high value (over 60-70 dinar) from shops in the souk.
Being a city in a Muslim country, alcohol may be rather hard to find and quite expensive, because of little demand. Some cafes and stores will sell wine and beer, since many locals also drink these beverages. Expect to pay 2-3 dinar for a 0.3 bottle of local beer (invariably Celtia brand), and 2-12 dinar for a bottle of local wine in a store (double in a bar). Hard alcohol is very hard to find and extremely expensive (more expensive than even in the Nordic Countries), since most locals avoid it. Your best bets are hotel bars (3-6 dinar for 50 ml of vodka or gin) and Magasin General supermarkets (state owned stores, the only ones authorized to sell hard liquor - one is located on 7 November avenue, near the Sousse Palace hotel). A bottle of gin or whiskey is about 80-120 dinar. No alcohol is sold on Fridays.
Sousse is one of few places in Tunisia with somewhat animated nightlife (mostly during high season though). In low season most of Sousse can be closed by 9:00pm. There are 2 kinds of places: normal bars, clubs, discos (upscale) and dodgy cabarets (low scale). The last ones are local oriented (music and crowd), and though might represent some interest as a phenomenon, are often frequented by hustlers, which, mixed with a cheap beer, tend to end up in arguments and mass fights (quickly resolved however). Many bars and discos are located in hotels, though most famous ones are standalone venues.
Living / Banana / Saloon disco. Free entrance, 5 TND beer, party time 0:00 - 04:00 everyday. Conveniently located in Sousse hotel zone near Samara hotel and Movenpick, these venues although themed differently (ambiance and music), share the same positioning ("VIP") and owner ("Bora-Bora" open air disco). More chilled touristic crowd; dress smart.
Be One / B1 club disco. Free entrance, 5 TND beer, party time 0:00 - 04:00 everyday. Located in Port Kantaoui near Houria Palace hotel and Vincci Resort. A sophisticated venue with nice relaxed and partying more tunisian crowd, european / arabic dance music, lots of couches, 2 bars, dancefloor and a high platform for cheeky girls to dance in the middle. In low seasons tends to get crowded by 02:00. Dress smart.
Edge bar. 4 TND beer, party time 23:00 - 02:00 everyday. Located in Cesar Palace hotel between Sousse and Port Kantaoui, Avenue 14 Janvier, near Les Oliviers. One of the many hotel bars (with separate entrance), this one though is somewhat classy with nice and relevant (4 stars hotel) more tunisian crowd, mixed european / arabic music. A good place for pre-party on your way to B1. Dress normal.
Don't compare the category directly to european hotels. Expect to take a star (or even two) from these hotels. 4/5 star hotels are recommended.
There's no danger on walking alone at any time, however most parts of town are abandoned after 9:00pm. Respect the locals and you will be respected. Crime is nearly non-existent, even if some of the neighborhoods of the city may look shabby or feel dangerous. Be aware for pickpockets when you walk in crowded areas, especially on the Camel market.
Expect some hassle in the souk (medina) and this is most normal. Merchants always try to show their goods/shops and see what you like. You have to get into the spirit to enjoy, always be nice and have a smile on your face. Even if sometimes annoying, this is absolutely not dangerous.
Women may want to avoid the red light area in the north west of the medina, reached through two overlapping walls which screen that street from the rest of the medina. Single women walking alone may be stared at, but, again, this is not dangerous, but rather a curiosity of some local men.
Most people who come up and speak English to you in the streets will be hoping to sell you something, no risk but end the conversation quickly to avoid them getting indignant when you dont buy, a simple 'non, merci' should suffice.
If you have a wrist band of your hotel, turn it inside out or wear something over it when going to the medina or shops. People will try to gain your trust by telling they work at the hotel you stay, with your wristband insideout you can test their story by asking the name of the hotel.