Ethiopia is a multilingual nation, with around 80 ethnolinguistic groups, the four largest of which are the Oromo, Amhara, Somali and Tigrayans. A majority of the population adheres to Christianity (mainly the Ethiopian Orthodox Tewahedo Church and P'ent'ay), while a third follow Islam, primarily Sunni. The country is the site of the Islamic Migration to Abyssinia and the oldest Muslim settlement in Africa, at Negash. The nation is a land of geographical contrasts, ranging from the vast fertile west, with its forests and numerous rivers, to the world's hottest settlement of Dallol in its north. The Ethiopian Highlands are the largest continuous mountain ranges in Africa, and the Sof Omar Caves contains the largest cave on the continent. Ethiopia also has the second-largest number of UNESCO World Heritage Sites in Africa. The sovereign state is a founding member of the UN, the Group of 24 (G-24), the Non-Aligned Movement, the G77 and the Organisation of African Unity. Addis Ababa serves as the headquarters of the African Union, the Pan African Chamber of Commerce and Industry, the United Nations Economic Commission for Africa, the African Standby Force and many of the global NGOs focused on Africa.