Obviously, this one isn't in use at the moment. We walked down one steep and winding stairwell to get to the bottom.
Right next door to the Nilometer, there's an Om Kalthoum museum. In terms of popularity, Om Kalthoum is like the Elvis of the Arab world. She was and still is WILDLY popular. She's well known across the globe, but especially loved here in Egypt since she was Egyptian.