It's named after a holy city and was kept inside a single Sufi brotherhood for nearly a century before it broke out onto every street corner in the country.
Café Touba is coffee ground together with djar (Guinea pepper/Selim), giving it a warm, peppery, almost incense-like flavor, poured theatrically between two cups to build up a foam. Street vendors sell it in small paper cups for a few cents on corners across Senegal.