At the southern tip of Roda Island, between the Manasterly Palace and the Um Kalthoum Museum, this well was used to measure the height of the Nile through the course of its annual fluctuations. Taxes could be calibrated from knowing the height of the floods, and the timing of the opening and closing of irrigation and drainage canals around the delta could be determined. Entering at the top, you can walk almost to the bottom by way of a narrow staircase cut into the side. The top is enclosed in an attractive 19th-century dome. The grounds around the Nilometer are relaxed and pleasant, with a view south up the river toward Dahab and, usually, a cool breeze off the water.