What you are looking at, is the largest mud-brick building, in the world. Protected as a UNESCO World Heritage Site since 1988, it is one of the most famous landmarks in Mali. Although, to be fair, there's not a lot of famous landmarks in Mali.
The Great Mosque dominates the city of Djenné, and a lot of care and effort goes into maintaining it. Considering it's made out of mud, it's not the most durable situation for when it rains. Like the other mud-brick buildings in Mali, every year the building needs to be repaired to maintain its condition.
The first mosque at this location was built around the 13th century. Its current incarnation dates back to 1907. The mosque is only open to Muslims though, so I didn't get a chance to go inside it.