Tunisia is celebrating on Thursday World Tourism Day under the theme "Tourism and Sustainable Energy: Powering Sustainable Development." Tourist regions all over the country will live through various festivities, including the cultural festival of the old city (Medina) of Tunis "Dream City," says the Tourism Ministry in a communiqué released Wednesday.   Hotels worked out entertainment programmes for tourists; national airports will celebrate the event through "a specific welcome to mark this event," the same source adds. At La Goulette Port, the Ministry announces the arrival of Italian cruise ship "MSC-Orchestra" with 3 500 tourists on board. Music and cultural shows will be performed by Tunisian and Italian troupes. Besides, a seminar is scheduled for Thursday morning in Tunis on "Tourism and Sustainable Energy."