This is considered one of the most important mosques in the Western Muslim world. One look through the main doorway will give you an idea of its immensity. With about 10,760 square feet, the Kairaouine was Morocco's largest mosque until Casablanca's Hassan II Mosque came along in the early 1990s. Built in AD 857 by Fatima, the daughter of a wealthy Kairaouine refugee, the mosque became the home of the West's first university and the world's foremost center of learning at the beginning of the second millennium. Stand at the entrance door's left side for a peek through the dozen horseshoe arches into the mihrab (marked by a hanging light). An east-facing alcove or niche used for leading prayer, the mihrab is rounded and covered with an arch designed to project sound back through the building. Lean in and look up to the brightly painted and intricately carved wood ceiling. If you're lucky enough to visit during the early morning cleaning, two huge wooden doors by the entrance swing open, providing a privileged view of the vast interior. For a good view of the courtyard, head to the rooftop of the Attarine Medersa.