It's a city in Mali. It was a famous crossroads of the Islamic world in North Africa back many centuries ago and there was a university there. Nowadays, there are a few mosques and the houses of some western explorers (e.g. Mungo Park) which have been turned into museums. And there is are manuscript repositories, which has something to do with the Unesco World Heritage people.

I admit to wanting to go there just because it sounds exotic and so "ends of the earth." Sort of like I went to Zanzibar (well, in that case it had to do with the theme song from the Patty Duke show).

More practically, it is the gateway for going to the Festival Au Desert, which is the main purpose of the trip.