Mali, famous for its mosque, which is the biggest mudbrick building in the world. As of 1987, the city had a population of 12,000. it has been recognized as a UNESCO World Heritage Site. UNESCO say on its website that "Djenné became a market centre and an important link in the trans-Saharan gold trade."
The best day to find transport to Djenné is Monday - market day - when many minibuses and bush taxis make their way to the town. Otherwise you may need to take transport to the Djenné junction on the main Bamako-Mopti road, and wait for further transport to Djenné.
For traveling short distances walking may be the best method as it allows you to appreciate the scenery and look at the mud based architecture in the city.
When the river is high, you can take a pinasse to nearby Fula villages.
On Tuesday morning there is a minibus to Bamako leaving at around 7:30 (7500CFA). (It may operate other mornings, too - I have no idea.)