Bab Zuweila is the southern gate of the Fatimid city, built in 1092 — the twin towers that once marked the boundary of medieval Cairo between the city and the suburbs. It served as the city's main public execution point during the Mamluk period; the heads of executed criminals and rebels were displayed on the spikes above the arch. Today it's one of the best experiences in Islamic Cairo: you can climb the minarets of the attached mosque (the Mosque of al-Mu'ayyad) for extraordinary views over the old city rooftops, minarets, and the street life of the tentmakers' bazaar below.
The view from the top of the minarets — 360 degrees of medieval Islamic city — is one of the best in Cairo. The climb is steep and the steps are old, but the reward is substantial. The tentmakers' bazaar (Khan el-Khayamiya) is immediately outside the gate, selling handmade appliqué textiles.