The view of the huge silver domes and needle-thin minarets of the Muhammad 'Ali Mosque against the stark backdrop of the desert cliffs of the Muquattam is one of Cairo's most striking visual icons. The mosque is just one feature of the Citadel, an immense fortified enclosure that housed the local power brokers from Salah al-Din, its 12th-century founder, to Napoléon in the 18th century and the British colonial governors and troops until their withdrawal in 1946. It served as the base of operations for Mamluk slave kings as well as for a series of sultans and pashas with their colorful retinues, including al-Nasir Muhammad's 1,200-concubine-strong harem.
The Citadel commands wonderful views of the city—smog permitting. From there, you can visit some impressive monuments, including the amazing Mosque and Madrasa of Sultan Hasan, one of the largest such structures in the world, and the remarkably calm, austere Mosque of Ibn Tulun, one of Cairo's oldest buildings.
The areas between these three mosques have been cut through with a series of main roads—including modern attempts to clear paths across the dense medieval urban fabric—and as a result, this part of the city lacks the coherence and charm of, say, Coptic Cairo or the area around Bab Zuwayla. Nevertheless, the scale and quality of these monuments is so impressive that if you have time to see only a few of Cairo's Islamic treasures, the Citadel and the Sultan Hasan and Ibn Tulun mosques should be among them.