Minarets spear the skyline in Kairouan, the morning air alive with the call to prayer, the holy city’s ochre walls warmed by the wakening Saharan sun. Among those minarets is the world’s oldest, belonging to the Great Mosque. Austere and imposing from without, a tour inside reveals a rich, subtly decorated building, that minaret displaying intricate carvings and inscriptions. The mosque was built in the 9th century, but glimpse inside the enormous prayer hall and you travel further back in time: many of its 400 columns were taken from other ancient sites in Tunisia, such as Carthage and El Jem. With the hubbub of the nearby souk, a mean line in sweets and pastries, and the best place in Tunisia to learn about the country's rich Islamic history, Kairouan quickly rewards exploration.