This is actually one of the most richly decorated mosques in Cairo, as it is one of the last great buildings built by the Mamluk sultans before Egypt was conquered by the Turkish Ottomans in the 16th century.
The beautiful facade of the building and the elaborate canopy of its entrance portal are faced by a nearly identical facade of the building opposite housing al-Ghuri's mausoleum (which requires its own entrance fee), thus framing the street in a kind of royal symmetry. (The only downside is that the street seemed to be under reconstruction at the time so it may be a bit messy.) The inside of the mosque is richly decorated with carved stone, marble paneling, painted ceilings, and a complex marble mosaic for the mihrab (prayer niche).
It's sometimes busy but like any other mosque you can visit outside prayer times and just give a small donation on your way out.
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