The most admired part of the Cairo Walls can be seen in the point in which the Street of Galal and the Street of Mansuriya and next to some parts of both the Northern walls and the Ayyubid wall. The walls extend for along distance till the other part of El-Azhar Park and then till Bab El-Wazir. Most of these walls were usually built either as a fortress to protect the city or to link the city with the citadel at the time of El Muiz Le Din Allah. This part has been reconstructed by Badr El Din El Gamali in the 11 Century. This part of the walls is admired for the handsomely designed tower of Burg El-Zafar that was renovated later by adding a long arrow slit. The interior part of this tower is rectangular in shape and is surmounted by a brick dome and on the right side appears a flight of stairs with nice star carvings on it. There is another gate few meters southward the tower known as El Bab El Gadid or the new gate. The beauty of this gate is accentuated by its bent entrance that was imitated in the religious and architectural buildings later.
You can get more information here.