Well, well. Here is a question requiring a whole article of its own, and I’ll tell you why. “African traditional religion” doesn’t quite exist. If you meant “Yoruba traditional religion”, I would still have a hard time answering you because the traditional Yorubas believed in so many things. In some cases, there were as many religions as there were family compounds, and each person believed in different things and worshiped them subsequently.
What I can say however is that there were some popular beliefs that have survived colonial intervention and modernity and are still being observed today in form of a system of belief. Their “holidays” are not usually public holidays but are usually marked with fanfare and festivities.
One of them is the Osun Osogbo Festival which is celebrated for about seven days in July/August in Osogbo, Nigeria. The festival is meant to celebrate a season of renewal and rebirth and it include dances, singing, and a ceremonial pilgrimage to the river Osun behind a virgin votary, the Arugba. (See photos from a previous Osun Osogbo festival here).
I also know of the Olojo Festival in Ile-Ife, and the Oke ‘Badan Festival in Ibadan which are also annual events.