Although this mosque is comparatively modern (built around in the late 19th century and the beginning of the 20th century), it's probably the most impressive and beautiful building of the neo-Mamluk style (the style imitating medieval Cairo architecture). Along with the much older but equally large Madrassa of Sultan Hassan next to it, it forms one of the most extraordinary set-pieces of Islamic Cairo.
There are several parts of the mosque you can see. From the outside, you enter by one of the side-portals facing the Sultan Hassan structure, but the mosque's original grand royal entrance can be seen on the north-west side (the side facing away from the Citadel), and is worth a look.
On the inside, the door in front of you leads to the tomb-chamber of Shaykh Ar-Rifa'i, a medieval sufi saint. On the right is the impressive and richly decorated prayer hall, which you should take a moment to wander around to admire the high dome at the centre, the ceilings, the grilled windows and the mihrab (the direction of Mecca). From here, a caretaker may offer to show you some of the otherwise locked-up mausoleums containing many different tombs of various royal family members. He'll expect a tip (10 pounds is good, but it's up to you), but it's worth it if you're not in a hurry.
Other than these, some of the most historically intriguing tombs are open without restriction when you turn left as you enter: the tomb of King Farouk, the last major king of Egypt (he abdicated in the 1952 coup, but his son, technically the last king of Egypt, ruled for less than a year), and the lavishly marbled mausoleum of the last Shah of Iran (who lived in exile after the 1979 revolution and was married to King Farouk's sister). An adjoining mausoleum contains the Shah's relatives but isn't always open.
At all times, throughout the building, make sure to look-up at the high ceilings which are richly decorated, or at the stone portals of the various entrances to the mosque.
This review is the subjective opinion of a TripAdvisor member and not of TripAdvisor LLC.