Ben Amera

Ben Amera is Africa's largest monolith, rising 633m above the desert floor. It's the world's second largest monolith only behind Uluru, in Australia. Ben Amera is located in Mauritania, near the border with Western Sahara. It lies 4km north of the train track where the famous Iron Ore Train travels between Nouâdibhou and Choûm.
Data from: en.wikipedia.org