Part of the original Fatimid fortifications, this massive gate surmounted on either side by the minarets of the Al-Muayyad Mosque was one of three main portals to the city. Painstakingly restored with USAID funding in 2001, it's the centerpiece of a plan to revive the area around the gate and is well worth a visit as part of a walk from Al Azhar Mosque to the Tentmakers' Souk. Over the years, the gate has been used as a venue for dancing, a cure for toothaches (driving a nail into the wood of the doors could apparently work magical wonders), and an execution ground (the last heads were displayed here at the beginning of the 19th century).
If you don't have time for a complete tour, at least walk through the gate, looking up as you pass between its massive doors. Local belief has it that the spirit of a certain Ottoman Sheikh Al Mitwali lives in the doorway, and it is possible that the model boat that hangs there is to provide him with transport to Mecca.
The tiny museum upstairs, which displays everyday items found during the excavation of the street around the door itself, is well worth a visit, particularly because the ticket includes access to the roof. From up here, you can get a much better idea of the layout of the neighborhood than you can from the crowded street below. You are also sure to notice the rickety wood structures on top of nearby buildings. These are pigeon coops, built to house the flocks of pet pigeons that you'll sometimes see circling at sunset.
Consider continuing past the Tentmakers' Souk toward The Citadel, the Madrasa Sultan Hassan, and the Mosque of Al Rifai to the decidedly scruffy neighborhood of Darb al Ahmar, which was an open field in the 11th century when the wall and gate were first constructed.