Sof Omar Cave is the longest cave in Ethiopia at 15.1 kilometres (9.4 mi) long; sources claim it is the longest system of caves in Africa.[1] 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.[2] It sinks at the Ayiew Maco entrance and reappears at the Holuca resurgence 1 kilometre (0.62 mi) away. According to tradition Sof Omar was the name of a Muslim holy man who lived in the area and Ayiew the name of his daughter. Maco and Holuca are local names for 'name' and 'cave', respectively. 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'.