It is a bit Chaotic to say "Islamic Cairo". there are at least 4 areas that can be called "Historical Islamic Cairo", and this depends on the dates it was built in:
1st: Fustat, this is the Mosque of Amr Ibn El-Aas, which was renovated in a very bad way, led to removing it from the UNESCO world heritage sights. However, the Mosque is the first mosque that was built in Africa and in Cairo od course. At this time, there was no Cairo still. The mosque is close to the Hanging Church, and other churches, and specially Abu Seifein Church and neighboring other 3 churches which is not guarded by Antiquity Police, and usually tourists miss.
2nd: Ibn Touloun, which was originally a Shiite mosque, and next to it is the wonderful Gayer Anderson House, which is a must to visit.
3rd is the famous Islamic Cairo, next to the Khan el-Khal;ilil market place, or Al-Azhar Mosque. Try to find Share' Al-Moez, (Al-Mo'ez st.) which includes 2/3rds of Islamic Antiquities. the street is too long, and it starts with Al-Hakem mosque, and ends with the Tent makers. Many people thing it has ended when they reach the main street, but not true. Cross the main street (and you will face the traffic of Cairo, which is wonder in itself), and then continue in Al-Ghouriyah street.
4th area is the Citadel and the Great Sultan Hassan church, and also Al-Refa'i mosque. This is an exception, as you have to pay a ticket..
The best place to eat is in the third part. Naguib Mahfous (Noble Prize winner) restaurant, a little bit expensive with Egyptian standards, and El-Dahan restaurant which is ok priced but not as Luxury like the first one.
This review is the subjective opinion of a TripAdvisor member and not of TripAdvisor LLC.