Sof Omar Caves, in Ethiopia, are on the Unesco Tentative list. By the way, the meeting to decide this year's new sites, will take place next month. I'm really looking foward to know the new world heritage sites.
At 15.1 kilometres (9.4 mi) long, Sof Omar Cave is the longest cave in Ethiopia; sources claim it is the longest system of caves in Africa and ranks as the 306th longest in the World. It is situated to the east of Robe, in the Bale Zone of the Oromia Region in southeastern Ethiopia, through which the Weyib River (Gestro River) flows. It sinks at the Ayiew Maco entrance and reappears at the Holuca resurgence 1 kilometre (0.62 mi) away. Long a religious centre, it is sacred both to Islam and the local Oromo traditional religion. The caves are known for their many pillars, particularly in the "Chamber of Columns". - in: wikipedia