Cairo, Egypt -- Lamps and careful plasterwork decorate the arches and capitals within the historic ibn Tulun mosque. Smaller arched openings are cut high in the walls of the arcades on the Qibla side of the mosque, both to admit light and to allow sound to travel unhindered (even slightly amplified) from the mihrab bay where the imam would deliver prayers and readings. © Rick Collier / RickCollier.com