Osun Osogbo Sacred Grove. Osogbo is the venue of the annual Osun-Osogbo festival along the River Osun. The festival is centered around the sacred grove of the river goddess Ọsun, a UNESCO World Heritage Site. In 1965 part of the Grove was declared a national monument, his was extended in 1992 so that the entire area is protected. Susan Wenger, an artist and Yoruban priestess was the leading advocate for the preservation of the grove.