The Great Mosque of Djenné, a UNESCO World Heritage Site, is the largest mud brick building in the world and a stunning example of Sudano-Sahelian architecture. Located in Djenné, Mali, it is most accessible via Mopti, from where you can take a bus or taxi to Djenné. The best time to visit is during the dry season from November to February to avoid heavy rains that can restrict access. While you can explore the town on your own, it's recommended to hire a local guide for insightful tours and to navigate the complex layout of the old town. Visiting the exterior is free, but typically only Muslims are allowed inside. Set aside at least half a day for the visit. It's crucial to respect local customs and note that photography of the mosque might require permission. The annual Crepissage festival, where locals replaster the mosque, is held in March or April and provides a unique cultural experience.